This commit brings following features:
Foreign key support from citus local tables to reference tables
* Foreign key support from reference tables to citus local tables
(only with RESTRICT & NO ACTION behavior)
* ALTER TABLE ENABLE/DISABLE trigger command support
* CREATE/DROP/ALTER trigger command support
and disallows:
* ALTER TABLE ATTACH/DETACH PARTITION commands
* CREATE TABLE <postgres table> ATTACH PARTITION <citus local table>
commands
* Foreign keys from postgres tables to citus local tables
(the other way was already disallowed)
for citus local tables.
Introduce table entry utility functions
Citus table cache entry utilities are introduced so that we can easily
extend existing functionality with minimum changes, specifically changes
to these functions. For example IsNonDistributedTableCacheEntry can be
extended for citus local tables without the need to scan the whole
codebase and update each relevant part.
* Introduce utility functions to find the type of tables
A table type can be a reference table, a hash/range/append distributed
table. Utility methods are created so that we don't have to worry about
how a table is considered as a reference table etc. This also makes it
easy to extend the table types.
* Add IsCitusTableType utilities
* Rename IsCacheEntryCitusTableType -> IsCitusTableTypeCacheEntry
* Change citus table types in some checks
Calling ErrorIfUnsupportedConstraint was still giving errors on Semmle. This
makes sure that we check for NULL at runtime. This way we can safely ignore all
errors created by this function.
Semmle reported quite some places where we use a value that could be NULL. Most of these are not actually a real issue, but better to be on the safe side with these things and make the static analysis happy.
Deparsing and parsing a query can be heavy on CPU. When locally executing
the query we don't need to do this in theory most of the time.
This PR is the first step in allowing to skip deparsing and parsing
the query in these cases, by lazily creating the query string and
storing the query in the task. Future commits will make use of this and
not deparse and parse the query anymore, but use the one from the task
directly.
DESCRIPTION: Distribute Types to worker nodes
When to propagate
==============
There are two logical moments that types could be distributed to the worker nodes
- When they get used ( just in time distribution )
- When they get created ( proactive distribution )
The just in time distribution follows the model used by how schema's get created right before we are going to create a table in that schema, for types this would be when the table uses a type as its column.
The proactive distribution is suitable for situations where it is benificial to have the type on the worker nodes directly. They can later on be used in queries where an intermediate result gets created with a cast to this type.
Just in time creation is always the last resort, you cannot create a distributed table before the type gets created. A good example use case is; you have an existing postgres server that needs to scale out. By adding the citus extension, add some nodes to the cluster, and distribute the table. The type got created before citus existed. There was no moment where citus could have propagated the creation of a type.
Proactive is almost always a good option. Types are not resource intensive objects, there is no performance overhead of having 100's of types. If you want to use them in a query to represent an intermediate result (which happens in our test suite) they just work.
There is however a moment when proactive type distribution is not beneficial; in transactions where the type is used in a distributed table.
Lets assume the following transaction:
```sql
BEGIN;
CREATE TYPE tt1 AS (a int, b int);
CREATE TABLE t1 AS (a int PRIMARY KEY, b tt1);
SELECT create_distributed_table('t1', 'a');
\copy t1 FROM bigdata.csv
```
Types are node scoped objects; meaning the type exists once per worker. Shards however have best performance when they are created over their own connection. For the type to be visible on all connections it needs to be created and committed before we try to create the shards. Here the just in time situation is most beneficial and follows how we create schema's on the workers. Outside of a transaction block we will just use 1 connection to propagate the creation.
How propagation works
=================
Just in time
-----------
Just in time propagation hooks into the infrastructure introduced in #2882. It adds types as a supported object in `SupportedDependencyByCitus`. This will make sure that any object being distributed by citus that depends on types will now cascade into types. When types are depending them self on other objects they will get created first.
Creation later works by getting the ddl commands to create the object by its `ObjectAddress` in `GetDependencyCreateDDLCommands` which will dispatch types to `CreateTypeDDLCommandsIdempotent`.
For the correct walking of the graph we follow array types, when later asked for the ddl commands for array types we return `NIL` (empty list) which makes that the object will not be recorded as distributed, (its an internal type, dependant on the user type).
Proactive distribution
---------------------
When the user creates a type (composite or enum) we will have a hook running in `multi_ProcessUtility` after the command has been applied locally. Running after running locally makes that we already have an `ObjectAddress` for the type. This is required to mark the type as being distributed.
Keeping the type up to date
====================
For types that are recorded in `pg_dist_object` (eg. `IsObjectDistributed` returns true for the `ObjectAddress`) we will intercept the utility commands that alter the type.
- `AlterTableStmt` with `relkind` set to `OBJECT_TYPE` encapsulate changes to the fields of a composite type.
- `DropStmt` with removeType set to `OBJECT_TYPE` encapsulate `DROP TYPE`.
- `AlterEnumStmt` encapsulates changes to enum values.
Enum types can not be changed transactionally. When the execution on a worker fails a warning will be shown to the user the propagation was incomplete due to worker communication failure. An idempotent command is shown for the user to re-execute when the worker communication is fixed.
Keeping types up to date is done via the executor. Before the statement is executed locally we create a plan on how to apply it on the workers. This plan is executed after we have applied the statement locally.
All changes to types need to be done in the same transaction for types that have already been distributed and will fail with an error if parallel queries have already been executed in the same transaction. Much like foreign keys to reference tables.
Following scenario resulted in distributed deadlock before this commit:
CREATE TABLE partitioning_test(id int, time date) PARTITION BY RANGE (time);
CREATE TABLE partitioning_test_2009 (LIKE partitioning_test);
CREATE TABLE partitioning_test_reference(id int PRIMARY KEY, subid int);
SELECT create_distributed_table('partitioning_test_2009', 'id'),
create_distributed_table('partitioning_test', 'id'),
create_reference_table('partitioning_test_reference');
ALTER TABLE partitioning_test ADD CONSTRAINT partitioning_reference_fkey FOREIGN KEY (id) REFERENCES partitioning_test_reference(id) ON DELETE CASCADE;
ALTER TABLE partitioning_test_2009 ADD CONSTRAINT partitioning_reference_fkey_2009 FOREIGN KEY (id) REFERENCES partitioning_test_reference(id) ON DELETE CASCADE;
ALTER TABLE partitioning_test ATTACH PARTITION partitioning_test_2009 FOR VALUES FROM ('2009-01-01') TO ('2010-01-01');
PG recently started propagating foreign key constraints
to partition tables. This came with a select query
to validate the the constaint.
We are already setting sequential mode execution for this
command. In order for validation select query to respect
this setting we need to explicitly set the GUC.
This commit also handles detach partition part.
The file handling the utility functions (DDL) for citus organically grew over time and became unreasonably large. This refactor takes that file and refactored the functionality into separate files per command. Initially modeled after the directory and file layout that can be found in postgres.
Although the size of the change is quite big there are barely any code changes. Only one two functions have been added for readability purposes:
- PostProcessIndexStmt which is extracted from PostProcessUtility
- PostProcessAlterTableStmt which is extracted from multi_ProcessUtility
A README.md has been added to `src/backend/distributed/commands` describing the contents of the module and every file in the module.
We need more documentation around the overloading of the COPY command, for now the boilerplate has been added for people with better knowledge to fill out.
Onur Tirtir
Halil Ozan Akgul
Naisila Puka
SaitTalhaNisanci
Jelte Fennema
Marco Slot
Hadi Moshayedi
Philip Dubé
Philip Dubé
Hadi Moshayedi
Nils Dijk
Onder Kalaci
Murat Tuncer
Jason Petersen
Hanefi Onaldi