This change adds the required infrastructure about metadata snapshot from MX
codebase into Citus, mainly metadata_sync.c file and master_metadata_snapshot UDF.
So far placements were assigned an Oid, but that was just used to track
insertion order. It also did so incompletely, as it was not preserved
across changes of the shard state. The behaviour around oid wraparound
was also not entirely as intended.
The newly introduced, explicitly assigned, IDs are preserved across
shard-state changes.
The prime goal of this change is not to improve ordering of task
assignment policies, but to make it easier to reference shards. The
newly introduced UpdateShardPlacementState() makes use of that, and so
will the in-progress connection and transaction management changes.
Related to #786
This change adds the `pg_dist_node` table that contains the information
about the workers in the cluster, replacing the previously used
`pg_worker_list.conf` file (or the one specified with `citus.worker_list_file`).
Upon update, `pg_worker_list.conf` file is read and `pg_dist_node` table is
populated with the file's content. After that, `pg_worker_list.conf` file
is renamed to `pg_worker_list.conf.obsolete`
For adding and removing nodes, the change also includes two new UDFs:
`master_add_node` and `master_remove_node`, which require superuser
permissions.
'citus.worker_list_file' guc is kept for update purposes but not used after the
update is finished.
related to a table that might be distributed, allowing any name
that is within regular PostgreSQL length limits to be extended
with a shard ID for use in shards on workers. Handles multi-byte
character boundaries in identifiers when making prefixes for
shard-extended names. Includes tests.
Uses hash_any from PostgreSQL's access/hashfunc.c.
Removes AppendShardIdToStringInfo() as it's used only once
and arguably is best replaced there with a call to AppendShardIdToName().
Adds UDF shard_name(object_name, shard_id) to expose the shard-extended
name logic to other PL/PGSQL, UDFs and scripts.
Bumps version to 6.0-2 to allow for UDF to be created in migration script.
Fixescitusdata/citus#781 and citusdata/citus#179.
hash_create(), called by TaskHashCreate(), doesn't work correctly for a
zero sized hash table. This triggers valgrind errors, and could
potentially cause crashes even without valgring.
This currently happens for Jobs with 0 tasks. These probably should be
optimized away before reaching TaskHashCreate(), but that's a bigger
change.
count_agg_clause *adds* the cost of the aggregates to the state
variable, it doesn't reinitialize it. That is intentional, as it is used
to incrementally add costs in some places.
is now a `::regtype` using the qualified name of the column type,
not the column type OID which may differ between master/worker nodes.
Test coverage of a hash reparitition using a UDT as the join column.
Note that the UDFs `worker_hash_partition_table` and `worker_range_partition_table`
are unchanged, and rightly expect an OID for the column type; but the
planner code building the commands now allows for `::regtype` casting
to do its magic.
Fixescitusdata/citus#111.
Fixescitusdata/citus#714
On `InsertShardRow`, we previously called `CommandCounterIncrement()` before
`CitusInvalidateRelcacheByRelid(relationId);`. This might prevent to skip
invalidation of the distributed table in the next access within the same session.
This commit enables to create different worker and master temporary folders.
This change is important for citus-mx on task-tracker execution. In simple words,
on citus-mx, the worker could actually be reponsible for the master tasks as well.
Prior to this change, both master and worker logic on task-tracker executor was
accessing and using the same files for different purposes which was dangerous on
certain cases (i.e., when task_tracker_delay is low).
Before this change, count on a distributed returned NULL if all shards
were pruned away, because on the master we replace with count(..) call
with a sum(..) call to sum the counts from the shards. However, sum
returns NULL when there are no rows, whereas count is expected to return
0.
I had changed these callbacks to use the same method I chose for the
router executor (for consistency), but as that method is flawed, we now
want to ensure we directly register them from PG_init as well.
Not entirely sure why we went with the shared memory hook approach, but
it causes problems (multiple registration) during crashes. Changing to
a simple direct registration call from PG_init.
An interaction between ReraiseRemoteError and DML transaction support
causes segfaults:
* ReraiseRemoteError calls PurgeConnection, freeing a connection...
* That connection is still in the xactParticipantHash
At transaction end, the memory in the freed connection might happen to
pass the "is this connection OK?" check, causing us to try to send an
ABORT over that connection. By removing it from the transaction hash
before calling ReraiseRemoteError, we avoid this possibility.
UNIQUE or PRIMARY KEY constraints. Also, properly propagate valid
EXCLUDE constraints to worker shard tables.
If an EXCLUDE constraint includes the distribution column,
the operator must be an equality operator.
Tests in regression suite for exclusion constraints that include
the partition column, omit it, and include it but with non-equality
operator. Regression tests also verify that valid exclusion constraints
are propagated to the shard tables. And the tests work in different
timezones now.
Fixescitusdata/citus#748 and citusdata/citus#778.
Three changes here to get to true multi-statement, multi-relation DDL
transactions (same functionality pre-5.2, with benefits of atomicity):
1. Changed the multi-shard utility hook to always run (consistency
with router executor hook, removes ad-hoc "installed" boolean)
2. Change the global connection list in multi_shard_transaction to
instead be a hash; update related functions to operate on global
hash instead of local hash/global list
3. Remove check within DDL code to prevent subsequent DDL commands;
place unset/reset guard around call to ConnectToNode to permit
connecting to additional nodes after DDL transaction has begun
In addition, code has been added to raise an error if a ROLLBACK TO
SAVEPOINT is attempted (similar to router executor), and comprehensive
tests execute all multi-DDL scenarios (full success, user ROLLBACK, any
actual errors (say, duplicate index), partial failure (duplicate index
on one node but not others), partial COMMIT (one node fails), and 2PC
partial PREPARE (one node fails)). Interleavings with other commands
(DML, \copy) are similarly all covered.
To permit use with ZomboDB (https://github.com/zombodb/zombodb), two
changes were necessary:
1. Permit use of `tableoid` system column in queries
2. Extend relation names appearing in index expressions
The first is accomplished by simply changing the deparse logic to allow
system columns in queries destined for distributed tables. The latter
was slightly more complex, given that DDL extension currently occurs on
workers. But since indexes cannot reference tables other than the one
being indexed, it is safe to look for any relation reference ending in
a '*' character and extend their penultimate segments with a shard id.
This change also adds an error to prevent users from distributing any
relations using the WITH (OIDS) feature, which is unsupported.
The call to hash_create specified HASH_CONTEXT without actually setting
one using the provided HASHCTL. The hashes returned by this function
are used locally, so simply using CurrentMemoryContext is sufficient.
In subquery pushdown, we allow outer joins if the join condition is on the
partition columns. WhereClauseList() used to return all join conditions including
outer joins. However, this has been changed with a commit related to outer join
support on regular queries. With this commit, we refactored ExtractFromExpressionWalker()
to return two lists of qualifiers. The first list is for inner join and filter
clauses and the second list is for outer join clauses. Therefore, we can also
use outer join clauses to check subquery pushdown prerequisites.
Before this change, we do not check whether given table which already contains any data
in master_create_distributed_table command. If that table contains any data, making it
it distributed, makes that data hidden to user. With this change, we now gave error to
user if the table contains data.
Recent changes to DDL and transaction logic resulted in a "regression"
from the viewpoint of users. Previously, DDL commands were allowed in
multi-command transaction blocks, though they were not processed in any
actual transactional manner. We improved the atomicity of our DDL code,
but added a restriction that DDL commands themselves must not occur in
any BEGIN/END transaction block.
To give users back the original functionality (and improved atomicity)
we now keep track of whether a multi-command transaction has modified
data (DML) or schema (DDL). Interleaving the two modification types in
a single transaction is disallowed.
This first step simply permits a single DDL command in such a block,
admittedly an incomplete solution, but one which will permit us to add
full multi-DDL command support in a subsequent commit.
I've been seeing warnings on OS X/clang for a while about these lines
and finally got tired of it. The main problem is that PRIu64 expects a
uint64_t but we were passing a uint64 (a PostgreSQL-defined type). In
PostgreSQL 9.5, we now have INT64_MODIFIER, so can build our own zero-
padded unsigned 64-bit int format modifier that expects a PostgreSQL-
provided uint64 type.
This simplifies the code slightly (no more ifdefs) and gets rid of the
warning that's been annoying me since April (my TODO creation time).
When an unreferenced prepared statement parameter does not explicitly
have a type assigned, we cannot deserialize it, to send to the remote
side. That commonly happens inside plpgsql functions, where local
variables are passed in as unused prepared statement parameters.
A recent change generates a "dummy" shard placement with its identifier
set to INVALID_SHARD_ID for SELECT queries against distributed tables
with no shards. Normally, no lock is acquired for SELECT statements,
but if all_modifications_commutative is set to true, we will acquire a
shared lock, triggering an assertion failure within LockShardResource
in the above case.
The "dummy" shard placement is actually necessary to ensure such empty
queries have somewhere to execute, and INVALID_SHARD_ID seems the most
appropriate value for the dummy's shard identifier field, so the most
straightforward fix is to just avoid locking invalid shard identifiers.
Eren Basak
Marco Slot
Andres Freund
Metin Doslu
Brian Cloutier
Onder Kalaci
Robin Thomas
Jason Petersen
Burak Yucesoy
Murat Tuncer
Eric B. Ridge