**DESCRIPTION:**
This pull request introduces the foundation and core logic for the
snapshot-based node split feature in Citus. This feature enables
promoting a streaming replica (referred to as a clone in this feature
and UI) to a primary node and rebalancing shards between the original
and the newly promoted node without requiring a full data copy.
This significantly reduces rebalance times for scale-out operations
where the new node already contains a full copy of the data via
streaming replication.
Key Highlights:
**1. Replica (Clone) Registration & Management Infrastructure**
Introduces a new set of UDFs to register and manage clone nodes:
- citus_add_clone_node()
- citus_add_clone_node_with_nodeid()
- citus_remove_clone_node()
- citus_remove_clone_node_with_nodeid()
These functions allow administrators to register a streaming replica of
an existing worker node as a clone, making it eligible for later
promotion via snapshot-based split.
**2. Snapshot-Based Node Split (Core Implementation)**
New core UDF:
- citus_promote_clone_and_rebalance()
This function implements the full workflow to promote a clone and
rebalance shards between the old and new primaries. Steps include:
1. Ensuring Exclusivity – Blocks any concurrent placement-changing
operations.
2. Blocking Writes – Temporarily blocks writes on the primary to ensure
consistency.
3. Replica Catch-up – Waits for the replica to be fully in sync.
4. Promotion – Promotes the replica to a primary using pg_promote.
5. Metadata Update – Updates metadata to reflect the newly promoted
primary node.
6. Shard Rebalancing – Redistributes shards between the old and new
primary nodes.
**3. Split Plan Preview**
A new helper UDF get_snapshot_based_node_split_plan() provides a preview
of the shard distribution post-split, without executing the promotion.
**Example:**
```
reb 63796> select * from pg_catalog.get_snapshot_based_node_split_plan('127.0.0.1',5433,'127.0.0.1',5453);
table_name | shardid | shard_size | placement_node
--------------+---------+------------+----------------
companies | 102008 | 0 | Primary Node
campaigns | 102010 | 0 | Primary Node
ads | 102012 | 0 | Primary Node
mscompanies | 102014 | 0 | Primary Node
mscampaigns | 102016 | 0 | Primary Node
msads | 102018 | 0 | Primary Node
mscompanies2 | 102020 | 0 | Primary Node
mscampaigns2 | 102022 | 0 | Primary Node
msads2 | 102024 | 0 | Primary Node
companies | 102009 | 0 | Clone Node
campaigns | 102011 | 0 | Clone Node
ads | 102013 | 0 | Clone Node
mscompanies | 102015 | 0 | Clone Node
mscampaigns | 102017 | 0 | Clone Node
msads | 102019 | 0 | Clone Node
mscompanies2 | 102021 | 0 | Clone Node
mscampaigns2 | 102023 | 0 | Clone Node
msads2 | 102025 | 0 | Clone Node
(18 rows)
```
**4 Test Infrastructure Enhancements**
- Added a new test case scheduler for snapshot-based split scenarios.
- Enhanced pg_regress_multi.pl to support creating node backups with
slightly modified options to simulate real-world backup-based clone
creation.
### 5. Usage Guide
The snapshot-based node split can be performed using the following
workflow:
**- Take a Backup of the Worker Node**
Run pg_basebackup (or an equivalent tool) against the existing worker
node to create a physical backup.
`pg_basebackup -h <primary_worker_host> -p <port> -D
/path/to/replica/data --write-recovery-conf
`
**- Start the Replica Node**
Start PostgreSQL on the replica using the backup data directory,
ensuring it is configured as a streaming replica of the original worker
node.
**- Register the Backup Node as a Clone**
Mark the registered replica as a clone of its original worker node:
`SELECT * FROM citus_add_clone_node('<clone_host>', <clone_port>,
'<primary_host>', <primary_port>);
`
**- Promote and Rebalance the Clone**
Promote the clone to a primary and rebalance shards between it and the
original worker:
`SELECT * FROM citus_promote_clone_and_rebalance('clone_node_id');
`
**- Drop Any Replication Slots from the Original Worker**
After promotion, clean up any unused replication slots from the original
worker:
`SELECT pg_drop_replication_slot('<slot_name>');
`
DESCRIPTION: Parallelizes shard rebalancing and removes the bottlenecks
that previously blocked concurrent logical-replication moves.
These improvements reduce rebalance windows—particularly for clusters
with large reference tables and enable multiple shard transfers to run in parallel.
Motivation:
Citus’ shard rebalancer has some key performance bottlenecks:
**Sequential Movement of Reference Tables:**
Reference tables are often assumed to be small, but in real-world
deployments, they can grow significantly large. Previously, reference
table shards were transferred as a single unit, making the process
monolithic and time-consuming.
**No Parallelism Within a Colocation Group:**
Although Citus distributes data using colocated shards, shard
movements within the same colocation group were serialized. In
environments with hundreds of distributed tables colocated
together, this serialization significantly slowed down rebalance
operations.
**Excessive Locking:**
Rebalancer used restrictive locks and redundant logical replication
guards, further limiting concurrency.
The goal of this commit is to eliminate these inefficiencies and enable
maximum parallelism during rebalance, without compromising correctness
or compatibility. Parallelize shard rebalancing to reduce rebalance
time.
Feature Summary:
**1. Parallel Reference Table Rebalancing**
Each reference-table shard is now copied in its own background task.
Foreign key and other constraints are deferred until all shards are
copied.
For single shard movement without considering colocation a new
internal-only UDF '`citus_internal_copy_single_shard_placement`' is
introduced to allow single-shard copy/move operations.
Since this function is internal, we do not allow users to call it
directly.
**Temporary Hack to Set Background Task Context** Background tasks
cannot currently set custom GUCs like application_name before executing
internal-only functions. 'citus_rebalancer ...' statement as a prefix in
the task command. This is a temporary hack to label internal tasks until
proper GUC injection support is added to the background task executor.
**2. Changes in Locking Strategy**
- Drop the leftover replication lock that previously serialized shard
moves performed via logical replication. This lock was only needed when
we used to drop and recreate the subscriptions/publications before each
move. Since Citus now removes those objects later as part of the “unused
distributed objects” cleanup, shard moves via logical replication can
safely run in parallel without additional locking.
- Introduced a per-shard advisory lock to prevent concurrent operations
on the same shard while allowing maximum parallelism elsewhere.
- Change the lock mode in AcquirePlacementColocationLock from
ExclusiveLock to RowExclusiveLock to allow concurrent updates within the
same colocation group, while still preventing concurrent DDL operations.
**3. citus_rebalance_start() enhancements**
The citus_rebalance_start() function now accepts two new optional
parameters:
```
- parallel_transfer_colocated_shards BOOLEAN DEFAULT false,
- parallel_transfer_reference_tables BOOLEAN DEFAULT false
```
This ensures backward compatibility by preserving the existing behavior
and avoiding any disruption to user expectations and when both are set
to true, the rebalancer operates with full parallelism.
**Previous Rebalancer Behavior:**
`SELECT citus_rebalance_start(shard_transfer_mode := 'force_logical');`
This would:
Start a single background task for replicating all reference tables
Then, move all shards serially, one at a time.
```
Task 1: replicate_reference_tables()
↓
Task 2: move_shard_1()
↓
Task 3: move_shard_2()
↓
Task 4: move_shard_3()
```
Slow and sequential. Reference table copy is a bottleneck. Colocated
shards must wait for each other.
**New Parallel Rebalancer:**
```
SELECT citus_rebalance_start(
shard_transfer_mode := 'force_logical',
parallel_transfer_colocated_shards := true,
parallel_transfer_reference_tables := true
);
```
This would:
- Schedule independent background tasks for each reference-table shard.
- Move colocated shards in parallel, while still maintaining dependency
order.
- Defer constraint application until all reference shards are in place.
-
```
Task 1: copy_ref_shard_1()
Task 2: copy_ref_shard_2()
Task 3: copy_ref_shard_3()
→ Task 4: apply_constraints()
↓
Task 5: copy_shard_1()
Task 6: copy_shard_2()
Task 7: copy_shard_3()
↓
Task 8-10: move_shard_1..3()
```
Each operation is scheduled independently and can run as soon as
dependencies are satisfied.
This PR provides successful build against PG18Beta1. RuleUtils PR was
reviewed separately: #8010
## PG 18Beta1–related changes for building Citus
### TupleDesc / Attr layout
**What changed in PG:** Postgres consolidated the
`TupleDescData.attrs[]` array into a more compact representation. Direct
field access (tupdesc->attrs[i]) was replaced by the new
`TupleDescAttr()` API.
**Citus adaptation:** Everywhere we previously used
`tupdesc->attrs[...]`, we now call `TupleDescAttr(tupdesc, idx)` (or our
own `Attr()` macro) under a compatibility guard.
*
5983a4cffc
General Logic:
* Use `Attr(...)` in places where `columnar_version_compat.h` is
included. This avoids the need to sprinkle `#if PG_VERSION_NUM` guards
around each attribute access.
* Use `TupleDescAttr(tupdesc, i)` when the relevant PostgreSQL header is
already included and the additional macro indirection is unnecessary.
### Collation‐aware `LIKE`
**What changed in PG:** The `textlike` operator now requires an explicit
collation, to avoid ambiguous‐collation errors. Core code switched from
`DirectFunctionCall2(textlike, ...)` to
`DirectFunctionCall2Coll(textlike, DEFAULT_COLLATION_OID, ...)`.
**Citus adaptation:** In `remote_commands.c` and any other LIKE call, we
now use `DirectFunctionCall2Coll(textlike, DEFAULT_COLLATION_OID, ...)`
and `#include <utils/pg_collation.h>`.
*
85b7efa1cd
### Columnar storage API
* Adapt `columnar_relation_set_new_filelocator` (and related init
routines) for PG 18’s revised SMGR and storage-initialization hooks.
* Pull in the new headers (`explain_format.h`,
`columnar_version_compat.h`) so the columnar module compiles cleanly
against PG 18.
- heap_modify_tuple + heap_inplace_update only exist on PG < 18; on PG18
the in-place helper was removed upstream
-
a07e03fd8f
### OpenSSL / TLS integration
**What changed in PG:** Moved from the legacy `SSL_library_init()` to
`OPENSSL_init_ssl(OPENSSL_INIT_LOAD_CONFIG, NULL)`, updated certificate
API calls (`X509_getm_notBefore`, `X509_getm_notAfter`), and
standardized on `TLS_method()`.
**Citus adaptation:** We now `#include <openssl/opensslv.h>` and use
`#if OPENSSL_VERSION_NUMBER >= 0x10100000L` to choose between`
OPENSSL_init_ssl()` or `SSL_library_init()`, and wrap`
X509_gmtime_adj()` calls around the new accessor functions.
*
6c66b7443c
### Adapt `ExtractColumns()` to the new PG-18 `expandRTE()` signature
PostgreSQL 18
80feb727c8
added a fourth argument of type `VarReturningType` to `expandRTE()`, so
calls that used the old 7-parameter form no longer compile. This patch:
* Wraps the `expandRTE(...)` call in a `#if PG_VERSION_NUM >= 180000`
guard.
* On PG 18+ passes the new `VAR_RETURNING_DEFAULT` argument before
`location`.
* On PG 15–17 continues to call the original 7-arg form.
* Adds the necessary includes (`parser/parse_relation.h` for `expandRTE`
and `VarReturningType`, and `pg_version_constants.h` for
`PG_VERSION_NUM`).
### Adapt `ExecutorStart`/`ExecutorRun` hooks to PG-18’s new signatures
PostgreSQL 18
525392d572
changed the signatures of the executor hooks:
* `ExecutorStart_hook` now returns `bool` instead of `void`, and
* `ExecutorRun_hook` drops its old `run_once` argument.
This patch preserves Citus’s existing hook logic by:
1. **Adding two adapter functions** under `#if PG_VERSION_NUM >=
PG_VERSION_18`:
* `citus_executor_start_adapter(QueryDesc *queryDesc, int eflags)`
Calls the old `CitusExecutorStart(queryDesc, eflags)` and then returns
`true` to satisfy the new hook’s `bool` return type.
* `citus_executor_run_adapter(QueryDesc *queryDesc, ScanDirection
direction, uint64 count)`
Calls the old `CitusExecutorRun(queryDesc, direction, count, true)`
(passing `true` for the dropped `run_once` argument), and returns
`void`.
2. **Installing the adapters** in `_PG_init()` instead of the original
hooks when building against PG 18+:
```c
#if PG_VERSION_NUM >= PG_VERSION_18
ExecutorStart_hook = citus_executor_start_adapter;
ExecutorRun_hook = citus_executor_run_adapter;
#else
ExecutorStart_hook = CitusExecutorStart;
ExecutorRun_hook = CitusExecutorRun;
#endif
```
### Adapt to PG-18’s removal of the “run\_once” flag from
ExecutorRun/PortalRun
PostgreSQL commit
[[3eea7a0](3eea7a0c97)
rationalized the executor’s parallelism logic by moving the “execute a
plan only once” check into `ExecutePlan()` itself and dropping the old
`bool run_once` argument from the public APIs:
```diff
- void ExecutorRun(QueryDesc *queryDesc,
- ScanDirection direction,
- uint64 count,
- bool run_once);
+ void ExecutorRun(QueryDesc *queryDesc,
+ ScanDirection direction,
+ uint64 count);
```
(and similarly for `PortalRun()`).
To stay compatible across PG 15–18, Citus now:
1. **Updates all internal calls** to `ExecutorRun(...)` and
`PortalRun(...)`:
* On PG 18+, use the new three-argument form (`ExecutorRun(qd, dir,
count)`).
* On PG 15–17, keep the old four-arg form (`ExecutorRun(qd, dir, count,
true)`) under a `#if PG_VERSION_NUM < 180000` guard.
2. **Guards the dispatcher hooks** via the adapter functions (from the
earlier patch) so that Citus’s executor hooks continue to work under
both the old and new signatures.
### Adapt to PG-18’s shortened PortalRun signature
PostgreSQL 18’s refactoring (see commit
[3eea7a0](3eea7a0c97))
also removed the old run_once and alternate‐dest arguments from the
public PortalRun() API. The signature changed from:
```diff
- bool PortalRun(Portal portal,
- long count,
- bool isTopLevel,
- bool run_once,
- DestReceiver *dest,
- DestReceiver *altdest,
- QueryCompletion *qc);
+ bool PortalRun(Portal portal,
+ long count,
+ bool isTopLevel,
+ DestReceiver *dest,
+ DestReceiver *altdest,
+ QueryCompletion *qc);
```
To support both versions in Citus, we:
1. **Version-guard each call** to `PortalRun()`:
* **On PG 18+** invoke the new 6-argument form.
* **On PG 15–17** fall back to the legacy 7-argument form, passing
`true` for `run_once`.
### Add support for PG-18’s new `plansource` argument in
`PortalDefineQuery`**
PostgreSQL 18 extended the `PortalDefineQuery` API to carry a
`CachedPlanSource *plansource` pointer so that the portal machinery can
track cached‐plan invalidation (as introduced alongside deferred-locking
in commit
525392d572.
To remain compatible across PG 15–18, Citus now wraps its calls under a
version guard:
```diff
- PortalDefineQuery(portal, NULL, sql, commandTag, plantree_list, NULL);
+#if PG_VERSION_NUM >= 180000
+ /* PG 18+: seven-arg signature (adds plansource) */
+ PortalDefineQuery(
+ portal,
+ NULL, /* no prepared-stmt name */
+ sql, /* the query text */
+ commandTag, /* the CommandTag */
+ plantree_list, /* List of PlannedStmt* */
+ NULL, /* no CachedPlan */
+ NULL /* no CachedPlanSource */
+ );
+#else
+ /* PG 15–17: six-arg signature */
+ PortalDefineQuery(
+ portal,
+ NULL, /* no prepared-stmt name */
+ sql, /* the query text */
+ commandTag, /* the CommandTag */
+ plantree_list, /* List of PlannedStmt* */
+ NULL /* no CachedPlan */
+ );
+#endif
```
### Adapt ExecInitRangeTable() calls to PG-18’s new signature
PostgreSQL commit
[cbc127917e04a978a788b8bc9d35a70244396d5b](cbc127917e)
overhauled the planner API for range‐table initialization:
**PG 18+**: added a fourth `Bitmapset *unpruned_relids` argument to
support deferred partition pruning
In Citus’s `create_estate_for_relation()` (in `columnar_metadata.c`), we
now wrap the call in a compile‐time guard so that the code compiles
correctly on all supported PostgreSQL versions:
```
/* Prepare permission info on PG 16+ */
#if PG_VERSION_NUM >= PG_VERSION_16
List *perminfos = NIL;
addRTEPermissionInfo(&perminfos, rte);
#else
List *perminfos = NIL; /* unused on PG 15 */
#endif
/* Initialize the range table, with the right signature for each PG version */
#if PG_VERSION_NUM >= PG_VERSION_18
/* PG 18+: four‐arg signature (adds unpruned_relids) */
ExecInitRangeTable(
estate,
list_make1(rte),
perminfos,
NULL /* unpruned_relids: not used by columnar */
);
#elif PG_VERSION_NUM >= PG_VERSION_16
/* PG 16–17: three‐arg signature (permInfos) */
ExecInitRangeTable(
estate,
list_make1(rte),
perminfos
);
#else
/* PG 15: two‐arg signature */
ExecInitRangeTable(
estate,
list_make1(rte)
);
#endif
estate->es_output_cid = GetCurrentCommandId(true);
```
### Adapt `pgstat_report_vacuum()` to PG-18’s new timestamp argument
PostgreSQL commit
[[30a6ed0ce4bb18212ec38cdb537ea4b43bc99b83](30a6ed0ce4)
extended the `pgstat_report_vacuum()` API by adding a `TimestampTz
start_time` parameter at the end so that the VACUUM statistics collector
can record when the operation began:
```diff
/* PG ≤17: four-arg signature */
- void pgstat_report_vacuum(Oid tableoid,
- bool shared,
- double num_live_tuples,
- double num_dead_tuples);
+/* PG ≥18: five-arg signature adds a start_time */
+ void pgstat_report_vacuum(Oid tableoid,
+ bool shared,
+ double num_live_tuples,
+ double num_dead_tuples,
+ TimestampTz start_time);
```
To support both versions, we now wrap the call in `columnar_tableam.c`
with a version guard, supplying `GetCurrentTimestamp()` for PG-18+:
```c
#if PG_VERSION_NUM >= 180000
/* PG 18+: include start_timestamp */
pgstat_report_vacuum(
RelationGetRelid(rel),
rel->rd_rel->relisshared,
Max(new_live_tuples, 0), /* live tuples */
0, /* dead tuples */
GetCurrentTimestamp() /* start time */
);
#else
/* PG 15–17: original signature */
pgstat_report_vacuum(
RelationGetRelid(rel),
rel->rd_rel->relisshared,
Max(new_live_tuples, 0), /* live tuples */
0 /* dead tuples */
);
#endif
```
### Adapt `ExecuteTaskPlan()` to PG-18’s expanded `CreateQueryDesc()`
signature
PostgreSQL 18 changed `CreateQueryDesc()` from an eight-argument to a
nine-argument call by inserting a `CachedPlan *cplan` parameter
immediately after the `PlannedStmt *plannedstmt` argument (see commit
525392d572).
To remain compatible with PG 15–17, Citus now wraps its invocation in
`local_executor.c` with a version guard:
```diff
- /* PG15–17: eight-arg CreateQueryDesc without cached plan */
- QueryDesc *queryDesc = CreateQueryDesc(
- taskPlan, /* PlannedStmt *plannedstmt */
- queryString, /* const char *sourceText */
- GetActiveSnapshot(),/* Snapshot snapshot */
- InvalidSnapshot, /* Snapshot crosscheck_snapshot */
- destReceiver, /* DestReceiver *dest */
- paramListInfo, /* ParamListInfo params */
- queryEnv, /* QueryEnvironment *queryEnv */
- 0 /* int instrument_options */
- );
+#if PG_VERSION_NUM >= 180000
+ /* PG18+: nine-arg CreateQueryDesc with a CachedPlan slot */
+ QueryDesc *queryDesc = CreateQueryDesc(
+ taskPlan, /* PlannedStmt *plannedstmt */
+ NULL, /* CachedPlan *cplan (none) */
+ queryString, /* const char *sourceText */
+ GetActiveSnapshot(),/* Snapshot snapshot */
+ InvalidSnapshot, /* Snapshot crosscheck_snapshot */
+ destReceiver, /* DestReceiver *dest */
+ paramListInfo, /* ParamListInfo params */
+ queryEnv, /* QueryEnvironment *queryEnv */
+ 0 /* int instrument_options */
+ );
+#else
+ /* PG15–17: eight-arg CreateQueryDesc without cached plan */
+ QueryDesc *queryDesc = CreateQueryDesc(
+ taskPlan, /* PlannedStmt *plannedstmt */
+ queryString, /* const char *sourceText */
+ GetActiveSnapshot(),/* Snapshot snapshot */
+ InvalidSnapshot, /* Snapshot crosscheck_snapshot */
+ destReceiver, /* DestReceiver *dest */
+ paramListInfo, /* ParamListInfo params */
+ queryEnv, /* QueryEnvironment *queryEnv */
+ 0 /* int instrument_options */
+ );
+#endif
```
### Adapt `RelationGetPrimaryKeyIndex()` to PG-18’s new “deferrable\_ok”
flag
PostgreSQL commit
14e87ffa5c
added a new Boolean `deferrable_ok` parameter to
`RelationGetPrimaryKeyIndex()` so that the lock manager can defer
unique‐constraint locks when requested. The API changed from:
```c
RelationGetPrimaryKeyIndex(Relation relation)
```
to:
```c
RelationGetPrimaryKeyIndex(Relation relation, bool deferrable_ok)
```
```diff
diff --git a/src/backend/distributed/metadata/node_metadata.c
b/src/backend/distributed/metadata/node_metadata.c
index e3a1b2c..f4d5e6f 100644
--- a/src/backend/distributed/metadata/node_metadata.c
+++ b/src/backend/distributed/metadata/node_metadata.c
@@ -2965,8 +2965,18 @@
*/
- Relation replicaIndex =
index_open(RelationGetPrimaryKeyIndex(pgDistNode),
- AccessShareLock);
+ #if PG_VERSION_NUM >= PG_VERSION_18
+ /* PG 18+ adds a bool "deferrable_ok" parameter */
+ Relation replicaIndex =
+ index_open(
+ RelationGetPrimaryKeyIndex(pgDistNode, false),
+ AccessShareLock);
+ #else
+ Relation replicaIndex =
+ index_open(
+ RelationGetPrimaryKeyIndex(pgDistNode),
+ AccessShareLock);
+ #endif
ScanKeyInit(&scanKey[0], Anum_pg_dist_node_nodename,
BTEqualStrategyNumber, F_TEXTEQ, CStringGetTextDatum(nodeName));
```
```diff
diff --git a/src/backend/distributed/operations/node_protocol.c b/src/backend/distributed/operations/node_protocol.c
index e3a1b2c..f4d5e6f 100644
--- a/src/backend/distributed/operations/node_protocol.c
+++ b/src/backend/distributed/operations/node_protocol.c
@@ -746,7 +746,12 @@
if (!OidIsValid(idxoid))
{
- idxoid = RelationGetPrimaryKeyIndex(rel);
+ /* Determine the index OID of the primary key (PG18 adds a second parameter) */
+#if PG_VERSION_NUM >= PG_VERSION_18
+ idxoid = RelationGetPrimaryKeyIndex(rel, false);
+#else
+ idxoid = RelationGetPrimaryKeyIndex(rel);
+#endif
}
return idxoid;
```
Because Citus has always taken the lock immediately—just as the old
two-arg call did—we pass `false` to keep that same immediate-lock
behavior. Passing `true` would switch to deferred locking, which we
don’t want.
### Adapt `ExplainOnePlan()` to PG-18’s expanded API
PostgreSQL 18 extended
525392d572
the `ExplainOnePlan()` function to carry the `CachedPlan *` and
`CachedPlanSource *` pointers plus an explicit `query_index`, letting
the EXPLAIN machinery track plan‐source invalidation. The old signature:
```c
/* PG ≤17 */
void
ExplainOnePlan(PlannedStmt *plannedstmt,
IntoClause *into,
struct ExplainState *es,
const char *queryString,
ParamListInfo params,
QueryEnvironment *queryEnv,
const instr_time *planduration,
const BufferUsage *bufusage);
```
became, in PG 18:
```c
/* PG ≥18 */
void
ExplainOnePlan(PlannedStmt *plannedstmt,
CachedPlan *cplan,
CachedPlanSource *plansource,
int query_index,
IntoClause *into,
struct ExplainState *es,
const char *queryString,
ParamListInfo params,
QueryEnvironment *queryEnv,
const instr_time *planduration,
const BufferUsage *bufusage,
const MemoryContextCounters *mem_counters);
```
To compile under both versions, Citus now wraps each call in
`multi_explain.c` with:
```c
#if PG_VERSION_NUM >= PG_VERSION_18
/* PG 18+: pass NULL for the new cached‐plan fields and zero for query_index */
ExplainOnePlan(
plan, /* PlannedStmt *plannedstmt */
NULL, /* CachedPlan *cplan */
NULL, /* CachedPlanSource *plansource */
0, /* query_index */
into, /* IntoClause *into */
es, /* ExplainState *es */
queryString, /* const char *queryString */
params, /* ParamListInfo params */
NULL, /* QueryEnvironment *queryEnv */
&planduration,/* const instr_time *planduration */
(es->buffers ? &bufusage : NULL),
(es->memory ? &mem_counters : NULL)
);
#elif PG_VERSION_NUM >= PG_VERSION_17
/* PG 17: same as before, plus passing mem_counters if enabled */
ExplainOnePlan(
plan,
into,
es,
queryString,
params,
queryEnv,
&planduration,
(es->buffers ? &bufusage : NULL),
(es->memory ? &mem_counters : NULL)
);
#else
/* PG 15–16: original seven-arg form */
ExplainOnePlan(
plan,
into,
es,
queryString,
params,
queryEnv,
&planduration,
(es->buffers ? &bufusage : NULL)
);
#endif
```
### Adapt to the unified “index interpretation” API in PG 18 (commit
a8025f544854)
PostgreSQL commit
a8025f5448
generalized the old btree‐specific operator‐interpretation API into a
single “index interpretation” interface:
* **Renamed type**:
`OpBtreeInterpretation` → `OpIndexInterpretation`
* **Renamed function**:
`get_op_btree_interpretation(opno)` →
`get_op_index_interpretation(opno)`
* **Unified field**:
Each interpretation now carries `cmptype` instead of `strategy`.
To build cleanly on PG 18 while still supporting PG 15–17, Citus’s
shard‐pruning code now wraps these changes:
```c
#include "pg_version_constants.h"
#if PG_VERSION_NUM >= PG_VERSION_18
/* On PG 18+ the btree‐only APIs vanished; alias them to the new generic versions */
typedef OpIndexInterpretation OpBtreeInterpretation;
#define get_op_btree_interpretation(opno) get_op_index_interpretation(opno)
#define ROWCOMPARE_NE COMPARE_NE
#endif
/* … later, when checking an interpretation … */
OpBtreeInterpretation *interp =
(OpBtreeInterpretation *) lfirst(cell);
#if PG_VERSION_NUM >= PG_VERSION_18
/* use cmptype on PG 18+ */
if (interp->cmptype == ROWCOMPARE_NE)
#else
/* use strategy on PG 15–17 */
if (interp->strategy == ROWCOMPARE_NE)
#endif
{
/* … */
}
```
### Adapt `create_foreignscan_path()` for PG-18’s revised signature
PostgreSQL commit
e222534679
reordered and removed a couple of parameters in the FDW‐path builder:
* **PG 15–17 signature (11 args)**
```c
create_foreignscan_path(PlannerInfo *root,
RelOptInfo *rel,
PathTarget *target,
double rows,
Cost startup_cost,
Cost total_cost,
List *pathkeys,
Relids required_outer,
Path *fdw_outerpath,
List *fdw_restrictinfo,
List *fdw_private);
```
* **PG 18+ signature (9 args)**
```c
create_foreignscan_path(PlannerInfo *root,
RelOptInfo *rel,
PathTarget *target,
double rows,
int disabled_nodes,
Cost startup_cost,
Cost total_cost,
Relids required_outer,
Path *fdw_outerpath,
List *fdw_private);
```
To support both, Citus now defines a compatibility macro in
`pg_version_compat.h`:
```c
#include "nodes/bitmapset.h" /* for Relids */
#include "nodes/pg_list.h" /* for List */
#include "optimizer/pathnode.h" /* for create_foreignscan_path() */
#if PG_VERSION_NUM >= PG_VERSION_18
/* PG18+: drop pathkeys & fdw_restrictinfo, add disabled_nodes */
#define create_foreignscan_path_compat(a, b, c, d, e, f, g, h, i, j, k) \
create_foreignscan_path( \
(a), /* root */ \
(b), /* rel */ \
(c), /* target */ \
(d), /* rows */ \
(0), /* disabled_nodes (unused by Citus) */ \
(e), /* startup_cost */ \
(f), /* total_cost */ \
(g), /* required_outer */ \
(h), /* fdw_outerpath */ \
(k) /* fdw_private */ \
)
#else
/* PG15–17: original signature */
#define create_foreignscan_path_compat(a, b, c, d, e, f, g, h, i, j, k) \
create_foreignscan_path( \
(a), (b), (c), (d), \
(e), (f), \
(g), (h), (i), (j), (k) \
)
#endif
```
Now every call to `create_foreignscan_path_compat(...)`—even in tests
like `fake_fdw.c`—automatically picks the correct argument list for
PG 15 through PG 18.
### Drop the obsolete bitmap‐scan hooks on PG 18+
PostgreSQL commit
c3953226a0
cleaned up the `TableAmRoutine` API by removing the two bitmap‐scan
callback slots:
* `scan_bitmap_next_block`
* `scan_bitmap_next_tuple`
Since those hook‐slots no longer exist in PG 18, Citus now wraps their
NULL‐initialization in a `#if PG_VERSION_NUM < PG_VERSION_18` guard. On
PG 15–17 we still explicitly set them to `NULL` (to satisfy the old
struct layout), and on PG 18+ we omit them entirely:
```c
#if PG_VERSION_NUM < PG_VERSION_18
/* PG 15–17 only: these fields were removed upstream in PG 18 */
.scan_bitmap_next_block = NULL,
.scan_bitmap_next_tuple = NULL,
#endif
```
### Adapt `vac_update_relstats()` invocation to PG-18’s new
“all\_frozen” argument
PostgreSQL commit
99f8f3fbbc
extended the `vac_update_relstats()` API by inserting a
`num_all_frozen_pages` parameter between the existing
`num_all_visible_pages` and `hasindex` arguments:
```diff
- /* PG ≤17: */
- void
- vac_update_relstats(Relation relation,
- BlockNumber num_pages,
- double num_tuples,
- BlockNumber num_all_visible_pages,
- bool hasindex,
- TransactionId frozenxid,
- MultiXactId minmulti,
- bool *frozenxid_updated,
- bool *minmulti_updated,
- bool in_outer_xact);
+ /* PG ≥18: adds num_all_frozen_pages */
+ void
+ vac_update_relstats(Relation relation,
+ BlockNumber num_pages,
+ double num_tuples,
+ BlockNumber num_all_visible_pages,
+ BlockNumber num_all_frozen_pages,
+ bool hasindex,
+ TransactionId frozenxid,
+ MultiXactId minmulti,
+ bool *frozenxid_updated,
+ bool *minmulti_updated,
+ bool in_outer_xact);
```
To compile cleanly on both PG 15–17 and PG 18+, Citus wraps its call in
a version guard and supplies a zero placeholder for the new field:
```c
#if PG_VERSION_NUM >= 180000
/* PG 18+: supply explicit “all_frozen” count */
vac_update_relstats(
rel,
new_rel_pages,
new_live_tuples,
new_rel_allvisible, /* allvisible */
0, /* all_frozen */
nindexes > 0,
newRelFrozenXid,
newRelminMxid,
&frozenxid_updated,
&minmulti_updated,
false /* in_outer_xact */
);
#else
/* PG 15–17: original signature */
vac_update_relstats(
rel,
new_rel_pages,
new_live_tuples,
new_rel_allvisible,
nindexes > 0,
newRelFrozenXid,
newRelminMxid,
&frozenxid_updated,
&minmulti_updated,
false /* in_outer_xact */
);
#endif
```
**Why all_frozen = 0?**
Columnar storage never embeds transaction IDs in its pages, so it never
needs to track “all‐frozen” pages the way a heap does. Setting both
allvisible and allfrozen to zero simply tells Postgres “there are no
pages with the visibility or frozen‐status bits set,” matching our
existing behavior.
This change ensures Citus’s VACUUM‐statistic updates work unmodified
across all supported Postgres versions.
Issue #7709 asks for security labels on columns to be propagated, to
support the `anon` extension. Before, Citus supported security labels
on roles (#7735) and this PR adds support for propagating security
labels on tables and columns.
All scenarios that involve propagating metadata for a Citus table now
include the security labels on the table and on the columns of the
table. These scenarios are:
- When a table becomes distributed using `create_distributed_table()` or
`create_reference_table()`, its security labels (if any) are propageted.
- When a security label is defined on a distributed table, or one of its
columns, the label is propagated.
- When a node is added to a Citus cluster, all distributed tables have
their security labels propagated.
- When a column of a distributed table is dropped, any security labels
on the column are also dropped.
- When a column is added to a distributed table, security labels can be
defined on the column and are propagated.
- Security labels on a distributed table or its columns are not
propagated when `citus.enable_metadata_sync` is enabled.
Regress test `seclabel` is extended with tests to cover these scenarios.
The implementation is somewhat involved because it impacts DDL
propagation of Citus tables, but can be broken down as follows:
- distributed_object_ops has `Role_SecLabel`, `Table_SecLabel` and
`Column_SecLabel` to take care of security labels on roles, tables and
columns. `Any_SecLabel` is used for all other security labels and is
essentially a nop.
- Deparser support - `DeparseRoleSecLabelStmt()`,
`DeparseTableSecLabelStmt()` and `DeparseColumnSecLabelStmt()` take care
of deparsing security label statements on roles, tables and columns
respectively.
- When reconstructing the DDL for a citus table, security labels on the
table or its columns are included by having
`GetPreLoadTableCreationCommands()` call a new function
`CreateSecurityLabelCommands()` to take care of any security labels on
the table or its columns.
- When changing a distributed table name to a shard name before running
a command locally on a worker, function `RelayEventExtendNames()` checks
for security labels on a table or its columns.
This is prep work for successful compilation with PG17
PG17added foreach_ptr, foreach_int and foreach_oid macros
Relevant PG commit
14dd0f27d7cd56ffae9ecdbe324965073d01a9ff
14dd0f27d7
We already have these macros, but they are different with the
PG17 ones because our macros take a DECLARED variable, whereas
the PG16 macros declare a locally-scoped loop variable themselves.
Hence I am renaming our macros to foreach_declared_
I am separating this into its own PR since it touches many files. The
main compilation PR is https://github.com/citusdata/citus/pull/7699
Fixes#6795
The `worker_copy_table_to_node` is not supposed to be called for Citus
tables. When this function was initially introduced in #6098 , it had
the respective check. But the check was omitted, since
`worker_copy_table_to_node` called for Citus table finishes with error
anyway:
```
ERROR: cannot execute a distributed query from a query on a shard
DETAIL: Executing a distributed query in a function call that may be pushed to a remote node can lead to incorrect results.
```
It turns out that in some cases this error does not occur. See #6795
I suggest restoring that check.
Co-authored-by: Karina Litskevich <litskevichkarina@gmail.com>
In preprocess phase, we save the original database name, replace
dbname field of CreatedbStmt with a temporary name (to let Postgres
to create the database with the temporary name locally) and then
we insert a cleanup record for the temporary database name on all
nodes **(\*\*)**.
And in postprocess phase, we first rename the temporary database
back to its original name for local node and then return a list of
distributed DDL jobs i) to create the database with the temporary
name and then ii) to rename it back to its original name on other
nodes. That way, if CREATE DATABASE fails on any of the nodes, the
temporary database will be cleaned up by the cleanup records that
we inserted in preprocess phase and in case of a failure, we won't
leak any databases called as the name that user intended to use for
the database.
Solves the problem documented in
https://github.com/citusdata/citus/issues/7369
for CREATE DATABASE commands.
**(\*\*):** To ensure that we insert cleanup records on all nodes,
with this PR we also start requiring having the coordinator in the
metadata because otherwise we would skip inserting a cleanup record
for the coordinator.
Rename InsertCleanupRecordInCurrentTransaction ->
InsertCleanupOnSuccessRecordInCurrentTransaction and hardcode policy
type as CLEANUP_DEFERRED_ON_SUCCESS.
Rename InsertCleanupRecordInSubtransaction ->
InsertCleanupRecordOutsideTransaction.
Moves the following functions to the Citus internal schema:
citus_internal_local_blocked_processes
citus_internal_global_blocked_processes
citus_internal_mark_node_not_synced
citus_internal_unregister_tenant_schema_globally
citus_internal_update_none_dist_table_metadata
citus_internal_update_placement_metadata
citus_internal_update_relation_colocation
citus_internal_start_replication_origin_tracking
citus_internal_stop_replication_origin_tracking
citus_internal_is_replication_origin_tracking_active
#7405
---------
Co-authored-by: Jelte Fennema-Nio <jelte.fennema@microsoft.com>
DESCRIPTION: citus_move_shard_placement now fails early when shard
cannot be safely moved
The implementation is quite simplistic -
`citus_move_shard_placement(...)` will fail with an error if there's any
new node in the cluster that doesn't have reference tables yet.
It could have been finer-grained, i.e. erroring only when trying to move
a shard to an unitialized node. Looking at the related functions -
`replicate_reference_tables()` or `citus_rebalance_start()`, I think
it's acceptable behaviour. These other functions also treat "any"
unitialized node as a temporary anomaly.
Fixes#7426
---------
Co-authored-by: Jelte Fennema-Nio <jelte.fennema@microsoft.com>
Moves the following functions:
citus_internal_delete_colocation_metadata
citus_internal_delete_partition_metadata
citus_internal_delete_placement_metadata
citus_internal_delete_shard_metadata
citus_internal_delete_tenant_schema
This change refactors the code by using generate_qualified_relation_name
from id instead of using a sequence of functions to generate the
relation name.
Fixes#6602
This change adds a script to programatically group all includes in a
specific order. The script was used as a one time invocation to group
and sort all includes throught our formatted code. The grouping is as
follows:
- System includes (eg. `#include<...>`)
- Postgres.h (eg. `#include "postgres.h"`)
- Toplevel imports from postgres, not contained in a directory (eg.
`#include "miscadmin.h"`)
- General postgres includes (eg . `#include "nodes/..."`)
- Toplevel citus includes, not contained in a directory (eg. `#include
"citus_verion.h"`)
- Columnar includes (eg. `#include "columnar/..."`)
- Distributed includes (eg. `#include "distributed/..."`)
Because it is quite hard to understand the difference between toplevel
citus includes and toplevel postgres includes it hardcodes the list of
toplevel citus includes. In the same manner it assumes anything not
prefixed with `columnar/` or `distributed/` as a postgres include.
The sorting/grouping is enforced by CI. Since we do so with our own
script there are not changes required in our uncrustify configuration.
We propagate `SECURITY LABEL [for provider] ON ROLE rolename IS
labelname` to the worker nodes.
We also make sure to run the relevant `SecLabelStmt` commands on a
newly added node by looking at roles found in `pg_shseclabel`.
See official docs for explanation on how this command works:
https://www.postgresql.org/docs/current/sql-security-label.html
This command stores the role label in the `pg_shseclabel` catalog table.
This commit also fixes the regex string in
`check_gucs_are_alphabetically_sorted.sh` script such that it escapes
the dot. Previously it was looking for all strings starting with "citus"
instead of "citus." as it should.
To test this feature, I currently make use of a special GUC to control
label provider registration in PG_init when creating the Citus extension.
DESCRIPTION: Adds support from issuing role management commands from worker nodes
It's unlikely to get into a distributed deadlock with role commands, we
don't care much about them at the moment.
There were several attempts to reduce the chances of a deadlock but we
didn't any of them merged into main branch yet, see:
#7325#7016#7009
I just enhanced the existing code to check if the relation is an index
belonging to a distributed table.
If so the shardId is appended to relation (index) name and the *_size
function are executed as before.
There is a change in an extern function:
`extern StringInfo GenerateSizeQueryOnMultiplePlacements(...)`
It's possible to create a new function and deprecate this one later if
compatibility is an issue.
Fixes https://github.com/citusdata/citus/issues/6496.
DESCRIPTION: Allows using Citus size functions on distributed tables
indexes.
---------
Co-authored-by: Onur Tirtir <onurcantirtir@gmail.com>
What we do to collect foreign key constraint commands in
WorkerCreateShardCommandList is quite similar to what we do in
CopyShardForeignConstraintCommandList. Plus, the code that we used
in WorkerCreateShardCommandList before was not able to properly handle
foreign key constraints between Citus local tables --when creating a
reference table from the referencing one.
With a few slight modifications made to
CopyShardForeignConstraintCommandList, we can use the same logic in
WorkerCreateShardCommandList too.
This PR provides successful compilation against PG16Beta2. It does some
necessary refactoring to prepare for full support of version 16, in
https://github.com/citusdata/citus/pull/6952 .
Change RelFileNode to RelFileNumber or RelFileLocator
Relevant PG commit
b0a55e43299c4ea2a9a8c757f9c26352407d0ccc
new header for varatt.h
Relevant PG commit:
d952373a987bad331c0e499463159dd142ced1ef
drop support for Abs, use fabs
Relevant PG commit
357cfefb09115292cfb98d504199e6df8201c957
tuplesort PGcommit: d37aa3d35832afde94e100c4d2a9618b3eb76472
Relevant PG commit:
d37aa3d35832afde94e100c4d2a9618b3eb76472
Fix vacuum in columnar
Relevant PG commit:
4ce3afb82ecfbf64d4f6247e725004e1da30f47c
older one:
b6074846cebc33d752f1d9a66e5a9932f21ad177
Add alloc_flags to pg_clean_ascii
Relevant PG commit:
45b1a67a0fcb3f1588df596431871de4c93cb76f
Merge GetNumConfigOptions() into get_guc_variables()
Relevant PG commit:
3057465acfbea2f3dd7a914a1478064022c6eecd
Minor PG refactor PG_FUNCNAME_MACRO __func__
Relevant PG commit
320f92b744b44f961e5d56f5f21de003e8027a7f
Pass NULL context to stringToQualifiedNameList, typeStringToTypeName
The pre-PG16 error behaviour for the following
stringToQualifiedNameList & typeStringToTypeName
was ereport(ERROR, ...)
Now with PG16 we have this context input. We preserve the same behaviour
by passing a NULL context, because of the following:
(copy paste comment from PG16)
If "context" isn't an ErrorSaveContext node, this behaves as
errstart(ERROR, domain), and the errsave() macro ends up acting
exactly like ereport(ERROR, ...).
Relevant PG commit
858e776c84f48841e7e16fba7b690b76e54f3675
Use RangeVarCallbackMaintainsTable instead of RangeVarCallbackOwnsTable
Relevant PG commit:
60684dd834a222fefedd49b19d1f0a6189c1632e
FIX THIS: Not implemented grant-level control of role inheritance
see PG commit
e3ce2de09d814f8770b2e3b3c152b7671bcdb83f
Make Scan node abstract
PG commit:
8c73c11a0d39049de2c1f400d8765a0eb21f5228
Change in Var representations, get_relids_in_jointree
PG commit
2489d76c4906f4461a364ca8ad7e0751ead8aa0d
Deadlock detection changes because SHM_QUEUE is removed
Relevant PG Commit:
d137cb52cb7fd44a3f24f3c750fbf7924a4e9532
TU_UpdateIndexes
Relevant PG commit
19d8e2308bc51ec4ab993ce90077342c915dd116
Use object_ownercheck and object_aclcheck functions
Relevant PG commits:
afbfc02983f86c4d71825efa6befd547fe81a926
c727f511bd7bf3c58063737bcf7a8f331346f253
Rework Permission Info for successful compilation
Relevant PG commits:
postgres/postgres@a61b1f7postgres/postgres@b803b7d
---------
Co-authored-by: onderkalaci <onderkalaci@gmail.com>
Index scans in PG16 return empty sets because of extra compatibility
enforcement for `ScanKeyInit` arguments.
Could be one of the relevant PG commits:
c8b2ef05f4
This PR fixes all incompatible `RegProcedure` and `Datum` arguments in
all `ScanKeyInit` functions used throughout the codebase.
Helpful for https://github.com/citusdata/citus/pull/6952
One problem with rebalancing by disk size is that shards in newly
created collocation groups are considered extremely small. This can
easily result in bad balances if there are some other collocation groups
that do have some data. One extremely bad example of this is:
1. You have 2 workers
2. Both contain about 100GB of data, but there's a 70MB difference.
3. You create 100 new distributed schemas with a few empty tables in
them
4. You run the rebalancer
5. Now all new distributed schemas are placed on the node with that had
70MB less.
6. You start loading some data in these shards and quickly the balance
is completely off
To address this edge case, this PR changes the by_disk_size rebalance
strategy to add a a base size of 100MB to the actual size of each
shard group. This can still result in a bad balance when shard groups
are empty, but it solves some of the worst cases.
This commit is the second and last phase of dropping PG13 support.
It consists of the following:
- Removes all PG_VERSION_13 & PG_VERSION_14 from codepaths
- Removes pg_version_compat entries and columnar_version_compat entries
specific for PG13
- Removes alternative pg13 test outputs
- Removes PG13 normalize lines and fix the test outputs based on that
It is a continuation of 5bf163a27d
citus_shard_sizes view had a shard name column we use to extract shard
id. This PR changes the column to shard id so we don't do unnecessary
string operation.
Creating a second PR to make reviewing easier.
This PR tests:
- replicate_reference_tables
- fix_partition_shard_index_names
- isolate_tenant_to_new_shard
- replicate_table_shards
DESCRIPTION: Fixes a bug in background shard rebalancer where the
replicate reference tables task fails if the current user is not a
superuser.
This change is to be backported to earlier releases. We should fix the
permissions for replicate_reference_tables on main branch such that it
can be run by non-superuser roles.
Fixes#6925.
Fixes#6926.
With this PR, we allow creating distributed tables with without
specifying a shard key via create_distributed_table(). Here are the
the important details about those tables:
* Specifying `shard_count` is not allowed because it is assumed to be 1.
* We mostly call such tables as "null shard-key" table in code /
comments.
* To avoid doing a breaking layout change in create_distributed_table();
instead of throwing an error, it will inform the user that
`distribution_type`
param is ignored unless it's explicitly set to NULL or 'h'.
* `colocate_with` param allows colocating such null shard-key tables to
each other.
* We define this table type, i.e., NULL_SHARD_KEY_TABLE, as a subclass
of
DISTRIBUTED_TABLE because we mostly want to treat them as distributed
tables in terms of SQL / DDL / operation support.
* Metadata for such tables look like:
- distribution method => DISTRIBUTE_BY_NONE
- replication model => REPLICATION_MODEL_STREAMING
- colocation id => **!=** INVALID_COLOCATION_ID (distinguishes from
Citus local tables)
* We assign colocation groups for such tables to different nodes in a
round-robin fashion based on the modulo of "colocation id".
Note that this PR doesn't care about DDL (except CREATE TABLE) / SQL /
operation (i.e., Citus UDFs) support for such tables but adds a
preliminary
API.
We are handling colocation groups with shard group count less than the
worker node count, using a method different than the usual rebalancer.
See #6739
While making the decision of using this method or not, we should've
ignored the nodes that are marked `shouldhaveshards = false`. This PR
excludes those nodes when making the decision.
Adds a test such that:
coordinator: []
worker 1: [1_1, 1_2]
worker 2: [2_1, 2_2]
(rebalance)
coordinator: []
worker 1: [1_1, 2_1]
worker 2: [1_2, 2_2]
If we take the coordinator into account, the rebalancer considers the
first state as balanced and does nothing (because shard_count <
worker_count)
But with this pr, we ignore the coordinator because it's
shouldhaveshards = false
So the rebalancer distributes each colocation group to both workers
Also, fixes an unrelated flaky test in the same file
DESCRIPTION: Fixes memory errors, caught by valgrind, of type
"conditional jump or move depends on uninitialized value"
When running Citus tests under Postgres with valgrind, the test cases
calling into `NonBlockingShardSplit` function produce valgrind errors of
type "conditional jump or move depends on uninitialized value".
The issue is caused by creating a HTAB in a wrong way. HASH_COMPARE flag
should have been used when creating a HTAB with user defined comparison
function. In the absence of HASH_COMPARE flag, HTAB falls back into
built-in string comparison function. However, valgrind somehow discovers
that the match function is not assigned to the user defined function as
intended.
Fixes#6835
DESCRIPTION: Adds control for background task executors involving a node
### Background and motivation
Nonblocking concurrent task execution via background workers was
introduced in [#6459](https://github.com/citusdata/citus/pull/6459), and
concurrent shard moves in the background rebalancer were introduced in
[#6756](https://github.com/citusdata/citus/pull/6756) - with a hard
dependency that limits to 1 shard move per node. As we know, a shard
move consists of a shard moving from a source node to a target node. The
hard dependency was used because the background task runner didn't have
an option to limit the parallel shard moves per node.
With the motivation of controlling the number of concurrent shard
moves that involve a particular node, either as source or target, this
PR introduces a general new GUC
citus.max_background_task_executors_per_node to be used in the
background task runner infrastructure. So, why do we even want to
control and limit the concurrency? Well, it's all about resource
availability: because the moves involve the same nodes, extra
parallelism won’t make the rebalance complete faster if some resource is
already maxed out (usually cpu or disk). Or, if the cluster is being
used in a production setting, the moves might compete for resources with
production queries much more than if they had been executed
sequentially.
### How does it work?
A new column named nodes_involved is added to the catalog table that
keeps track of the scheduled background tasks,
pg_dist_background_task. It is of type integer[] - to store a list
of node ids. It is NULL by default - the column will be filled by the
rebalancer, but we may not care about the nodes involved in other uses
of the background task runner.
Table "pg_catalog.pg_dist_background_task"
Column | Type
============================================
job_id | bigint
task_id | bigint
owner | regrole
pid | integer
status | citus_task_status
command | text
retry_count | integer
not_before | timestamp with time zone
message | text
+nodes_involved | integer[]
A hashtable named ParallelTasksPerNode keeps track of the number of
parallel running background tasks per node. An entry in the hashtable is
as follows:
ParallelTasksPerNodeEntry
{
node_id // The node is used as the hash table key
counter // Number of concurrent background tasks that involve node node_id
// The counter limit is citus.max_background_task_executors_per_node
}
When the background task runner assigns a runnable task to a new
executor, it increments the counter for each of the nodes involved with
that runnable task. The limit of each counter is
citus.max_background_task_executors_per_node. If the limit is reached
for any of the nodes involved, this runnable task is skipped. And then,
later, when the running task finishes, the background task runner
decrements the counter for each of the nodes involved with the done
task. The following functions take care of these increment-decrement
steps:
IncrementParallelTaskCountForNodesInvolved(task)
DecrementParallelTaskCountForNodesInvolved(task)
citus.max_background_task_executors_per_node can be changed in the
fly. In the background rebalancer, we simply give {source_node,
target_node} as the nodesInvolved input to the
ScheduleBackgroundTask function. The rest is taken care of by the
general background task runner infrastructure explained above. Check
background_task_queue_monitor.sql and
background_rebalance_parallel.sql tests for detailed examples.
#### Note
This PR also adds a hard node dependency if a node is first being used
as a source for a move, and then later as a target. The reason this
should be a hard dependency is that the first move might make space for
the second move. So, we could run out of disk space (or at least
overload the node) if we move the second shard to it before the first
one is moved away.
Fixes https://github.com/citusdata/citus/issues/6716
DESCRIPTION: Refactor and unify shard move and copy functions
Shard move and copy functions share a lot of code in common. This PR
unifies these functions into one, along with some helper functions. To
preserve the current behavior, we'll introduce and use an enum
parameter, and hardcoded strings for producing error/warning messages.
This pull request proposes a change to the logic used for propagating
identity columns to worker nodes in citus. Instead of creating a
dependent sequence for each identity column and changing its default
value to `nextval(seq)/worker_nextval(seq)`, this update will pass the
identity columns as-is to the worker nodes.
Please note that there are a few limitations to this change.
1. Only bigint identity columns will be allowed in distributed tables to
ensure compatibility with the DDL from any node functionality. Our
current distributed sequence implementation only allows insert
statements from all nodes for bigint sequences.
2. `alter_distributed_table` and `undistribute_table` operations will
not be allowed for tables with identity columns. This is because we do
not have a proper way of keeping sequence states consistent across the
cluster.
DESCRIPTION: Prevents using identity columns on data types other than
`bigint` on distributed tables
DESCRIPTION: Prevents using `alter_distributed_table` and
`undistribute_table` UDFs when a table has identity columns
DESCRIPTION: Fixes a bug that prevents enforcing identity column
restrictions on worker nodes
Depends on #6740Fixes#6694
DESCRIPTION: This PR removes the task dependencies between shard moves
for which the shards belong to different colocation groups. This change
results in scheduling multiple tasks in the RUNNABLE state. Therefore it
is possible that the background task monitor can run them concurrently.
Previously, all the shard moves planned in a rebalance operation took
dependency on each other sequentially.
For instance, given the following table and shards
colocation group 1 colocation group 2
table1 table2 table3 table4 table 5
shard11 shard21 shard31 shard41 shard51
shard12 shard22 shard32 shard42 shard52
if the rebalancer planner returned the below set of moves
` {move(shard11), move(shard12), move(shard41), move(shard42)}`
background rebalancer scheduled them such that they depend on each other
sequentially.
```
{move(reftables) if there is any, none}
|
move( shard11)
|
move(shard12)
| {move(shard41)<--- move(shard12)} This is an artificial dependency
move(shard41)
|
move(shard42)
```
This results in artificial dependencies between otherwise independent
moves.
Considering that the shards in different colocation groups can be moved
concurrently, this PR changes the dependency relationship between the
moves as follows:
```
{move(reftables) if there is any, none} {move(reftables) if there is any, none}
| |
move(shard11) move(shard41)
| |
move(shard12) move(shard42)
```
---------
Co-authored-by: Jelte Fennema <jelte.fennema@microsoft.com>
Description:
Implementing CDC changes using Logical Replication to avoid
re-publishing events multiple times by setting up replication origin
session, which will add "DoNotReplicateId" to every WAL entry.
- shard splits
- shard moves
- create distributed table
- undistribute table
- alter distributed tables (for some cases)
- reference table operations
The citus decoder which will be decoding WAL events for CDC clients,
ignores any WAL entry with replication origin that is not zero.
It also maps the shard names to distributed table names.
DESCRIPTION: Check before logicalrep for rebalancer, error if needed
Check if we can use logical replication or not, in case of shard
transfer mode = auto, before executing the shard moves. If we can't,
error out. Before this PR, we used to error out in the middle of shard
moves:
```sql
set citus.shard_count = 4; -- just to get the error sooner
select citus_remove_node('localhost',9702);
create table t1 (a int primary key);
select create_distributed_table('t1','a');
create table t2 (a bigint);
select create_distributed_table('t2','a');
select citus_add_node('localhost',9702);
select rebalance_table_shards();
NOTICE: Moving shard 102008 from localhost:9701 to localhost:9702 ...
NOTICE: Moving shard 102009 from localhost:9701 to localhost:9702 ...
NOTICE: Moving shard 102012 from localhost:9701 to localhost:9702 ...
ERROR: cannot use logical replication to transfer shards of the relation t2 since it doesn't have a REPLICA IDENTITY or PRIMARY KEY
```
Now we check and error out in the beginning, without moving the shards.
fixes: #6727
DESCRIPTION: Fixes a bug in shard copy operations.
For copying shards in both shard move and shard split operations, Citus
uses the COPY statement.
A COPY all statement in the following form
` COPY target_shard FROM STDIN;`
throws an error when there is a GENERATED column in the shard table.
In order to fix this issue, we need to exclude the GENERATED columns in
the COPY and the matching SELECT statements. Hence this fix converts the
COPY and SELECT all statements to the following form:
```
COPY target_shard (col1, col2, ..., coln) FROM STDIN;
SELECT (col1, col2, ..., coln) FROM source_shard;
```
where (col1, col2, ..., coln) does not include a GENERATED column.
GENERATED column values are created in the target_shard as the values
are inserted.
Fixes#6705.
---------
Co-authored-by: Teja Mupparti <temuppar@microsoft.com>
Co-authored-by: aykut-bozkurt <51649454+aykut-bozkurt@users.noreply.github.com>
Co-authored-by: Jelte Fennema <jelte.fennema@microsoft.com>
Co-authored-by: Gürkan İndibay <gindibay@microsoft.com>
DESCRIPTION: Adds logic to distribute unbalanced shards
If the number of shard placements (for a colocation group) is less than
the number of workers, it means that some of the workers will remain
empty. With this PR, we consider these shard groups as a colocation
group, in order to make them be distributed evenly as much as possible
across the cluster.
Example:
```sql
create table t1 (a int primary key);
create table t2 (a int primary key);
create table t3 (a int primary key);
set citus.shard_count =1;
select create_distributed_table('t1','a');
select create_distributed_table('t2','a',colocate_with=>'t1');
select create_distributed_table('t3','a',colocate_with=>'t2');
create table tb1 (a bigint);
create table tb2 (a bigint);
select create_distributed_table('tb1','a');
select create_distributed_table('tb2','a',colocate_with=>'tb1');
select citus_add_node('localhost',9702);
select rebalance_table_shards();
```
Here we have two colocation groups, each with one shard group. Both
shard groups are placed on the first worker node. When we add a new
worker node and try to rebalance table shards, the rebalance planner
considers it well balanced and does nothing. With this PR, the
rebalancer tries to distribute these shard groups evenly across the
cluster as much as possible. For this example, with this PR, the
rebalancer moves one of the shard groups to the second worker node.
fixes: #6715
Muhammad Usama
Mehmet YILMAZ
Colm
Cédric Villemain
naisila
Naisila Puka
Karina
eaydingol
Onur Tirtir
Filip Sedlák
Nils Dijk
Cédric Villemain
zhjwpku
ahmet gedemenli
Jelte Fennema
Halil Ozan Akgül
Gokhan Gulbiz
Emel Şimşek
rajeshkt78