PostgreSQL 17 seems to have introduced improvements in how correlated
subqueries are handled during plan generation. Instead of generating a
trivial subplan with WHERE true, it now applies more specific filtering
(WHERE (key = 5)), which makes the execution plan more efficient.
https://github.com/postgres/postgres/commit/b262ad44
```
diff -dU10 -w /__w/citus/citus/src/test/regress/expected/local_table_join.out /__w/citus/citus/src/test/regress/results/local_table_join.out
--- /__w/citus/citus/src/test/regress/expected/local_table_join.out.modified 2024-11-05 09:53:50.423970699 +0000
+++ /__w/citus/citus/src/test/regress/results/local_table_join.out.modified 2024-11-05 09:53:50.463971296 +0000
@@ -1420,32 +1420,32 @@
) as subq_1
) as subq_2;
DEBUG: Wrapping relation "custom_pg_type" to a subquery
DEBUG: generating subplan 204_1 for subquery SELECT typdefault FROM local_table_join.custom_pg_type WHERE true
ERROR: direct joins between distributed and local tables are not supported
HINT: Use CTE's or subqueries to select from local tables and use them in joins
-- correlated sublinks are not yet supported because of #4470, unless we convert not-correlated table
SELECT COUNT(*) FROM distributed_table d1 JOIN postgres_table using(key)
WHERE d1.key IN (SELECT key FROM distributed_table WHERE d1.key = key and key = 5);
DEBUG: Wrapping relation "postgres_table" to a subquery
-DEBUG: generating subplan XXX_1 for subquery SELECT key FROM local_table_join.postgres_table WHERE true
+DEBUG: generating subplan 206_1 for subquery SELECT key FROM local_table_join.postgres_table WHERE (key OPERATOR(pg_catalog.=) 5)
```
Co-authored-by: Naisila Puka <37271756+naisila@users.noreply.github.com>
PG16 compatibility - part 9
Check out part 1 42d956888d
part 2 0d503dd5ac
part 3 907d72e60d
part 4 7c6b4ce103
part 5 6056cb2c29
part 6 b36c431abb
part 7 ee3153fe50
part 8 2c50b5f7ff
This commit is in the series of PG16 compatibility commits. It makes some changes
to our tests in order to be compatible with the following in PG16:
- Fix multi_subquery_in_where_reference_clause test
somehow PG got rid of the outer join
(e.g., explain doesn't show outer joins),
hence we can pushdown the subquery.
Changing to users_reference_table
- Fix unqualified column names for views in PG16
Relevant PG commit:
47bb9db759
47bb9db75996232ea71fc1e1888ffb0e70579b54
- Fix global_cancel test
Error wording and detail changed
Relevant PG commit:
2631ebab7b
2631ebab7b18bdc079fd86107c47d6104a6b3c6e
- Fix local_table_join_test with lateral subquery
Possible relevant PG commit:
ae89129aa3
ae89129aa3555c263b8c3ccc4c0f1ef7e46201aa
I removed the where clause and the limit count error was hit again.
With the where clause the query unexpectedly works.
- Fix test outputs
Relevant PG commits:
-- 1349d2790b
-- f4c7c410ee
For multi_explain and multi_complex_count_distinct there were too many places
touched so I just added an alternative test output.
For the other tests I modified the problematic parts.
More PG16 compatibility commits are coming soon ...
Changes test files in multi and multi-1 schedules such that they
accomodate coordinator in metadata.
Changes fall into the following buckets:
1. When coordinator is in metadata, reference table shards are present
in coordinator too.
This changes test outputs checking the table size, shard numbers etc.
for reference tables.
2. When coordinator is in metadata, postgres tables are converted to
citus local tables whenever a foreign key relationship to them is
created. This changes some test cases which tests it should not be
possible to create foreign keys to postgres tables.
3. Remove lines that add/remove coordinator for testing purposes.
We should do the sublink conversations at the end of the recursive
planning because earlier steps might have transformed the query into a
shape that needs recursively planning the sublinks.
DESCRIPTION: Fixes early sublink check at recursive planner.
Related to PR https://github.com/citusdata/citus/pull/6650
Adds support for propagating create/drop view commands and views to
worker node while scaling out the cluster. Since views are dropped while
converting the table type, metadata connection will be used while
propagating view commands to not switch to sequential mode.
With the introduction of #4385 we inadvertently started allowing and
pushing down certain lateral subqueries that were unsafe to push down.
To be precise the type of LATERAL subqueries that is unsafe to push down
has all of the following properties:
1. The lateral subquery contains some non recurring tuples
2. The lateral subquery references a recurring tuple from
outside of the subquery (recurringRelids)
3. The lateral subquery requires a merge step (e.g. a LIMIT)
4. The reference to the recurring tuple should be something else than an
equality check on the distribution column, e.g. equality on a non
distribution column.
Property number four is considered both hard to detect and probably not
used very often. Thus this PR ignores property number four and causes
query planning to error out if the first three properties hold.
Fixes#5327
It seems that we need to consider only pseudo constants while doing some
shortcuts in planning. For example there could be a false clause but it
can contribute to the result in which case it will not be a pseudo
constant.
We would exclude tables without relationRestriction from conversion
candidates in local-distributed table joins. This could leave a leftover
local table which should have been converted to a subquery.
Ideally I would expect that in each call to CreateDistributedPlan we
would pass a new plan id, but that seems like a bigger change.
Attribute number in a subquery RTE and relation RTE means different
things. In a relation attribute number will point to the column number
in the table definition including the dropped columns as well however in
subquery, it means the index in the target list. When we convert a
relation RTE to subquery RTE we should either correct all the relevant
attribute numbers or we can just add a dummy column for the dropped
columns. We choose the latter in this commit because it is practically
too vulnerable to update all the vars in a query.
Another thing this commit fixes is that in case a join restriction
clause list contains a false clause, we should just returns a false
clause instead of the whole list, because the whole list will contain
restrictions from other RTEs as well and this breaks the query, which
can be seen from the output changes, now it is much simpler.
Also instead of adding single tests for dropped columns, we choose to
run the whole mixed queries with tables with dropped columns, this
revealed some bugs already, which are fixed in this commit.
Instead of sending NULL's over a network, we now convert the subqueries
in the form of:
SELECT t.a, NULL, NULL FROM (SELECT a FROM table)t;
And we recursively plan the inner part so that we don't send the NULL's
over network. We still need the NULLs in the outer subquery because we
currently don't have an easy way of updating all the necessary places in
the query.
Add some documentation for how the conversion is done
It seems that most of the updates were broken, we weren't aware of it
because there wasn't any data in the tables. They are broken mostly
because local tables do not have a shard id and some code paths should
be updated with that information, currently when there is an invalid
shard id, it is assumed to be pruned.
Consider local tables in router planner
In case there is a local table, the shard id will not be valid and there
are some checks that rely on shard id, we should skip these in case of
local tables, which is handled with a dummy placement.
Add citus local table dist table join tests
add local-dist table mixed joins tests
AllDataLocallyAccessible and ContainsLocalTableSubqueryJoin are removed.
We can possibly remove ModifiesLocalTableWithRemoteCitusLocalTable as
well. Though this removal has a side effect that now when all the data
is locally available, we could still wrap a relation into a subquery, I
guess that should be resolved in the router planner itself.
Add more tests
When we wrap an RTE to subquery we are updating the variables varno's as
1, however we should also update the varno's of vars in quals.
Also some other small code quality improvements are done.
The previous algorithm was not consistent and it could convert different
RTEs based on the table orders in the query. Now we convert local tables
if there is a distributed table which doesn't have a unique index. So if
there are 4 tables, local1, local2, dist1, dist2_with_pkey then we will
convert local1 and local2 in `auto` mode. Converting a distributed table
is not that logical because as there is a distributed table without a
unique index, we will need to convert the local tables anyway. So
converting the distributed table with pkey is redundant.
Remove FillLocalAndDistributedRTECandidates and use
ShouldConvertLocalTableJoinsToSubqueries, which simplifies things as we
rely on a single function to decide whether we should continue
converting RTE to subquery.
We should not recursively plan an already routable plannable query. An
example of this is (SELECT * FROM local JOIN (SELECT * FROM dist) d1
USING(a));
So we let the recursive planner do all of its work and at the end we
convert the final query to to handle unsupported joins. While doing each
conversion, we check if it is router plannable, if so we stop.
Only consider range table entries that are in jointree
If a range table is not in jointree then there is no point in
considering that because we are trying to convert range table entries to
subqueries for join use case.
Check equality in quals
We want to recursively plan distributed tables only if they have an
equality filter on a unique column. So '>' and '<' operators will not
trigger recursive planning of distributed tables in local-distributed
table joins.
Recursively plan distributed table only if the filter is constant
If the filter is not a constant then the join might return multiple rows
and there is a chance that the distributed table will return huge data.
Hence if the filter is not constant we choose to recursively plan the
local table.
When doing local-distributed table joins we convert one of them to
subquery. The current policy is that we convert distributed tables to
subquery if it has a unique index on a column that has unique
index(primary key also has a unique index).
Mehmet YILMAZ
Naisila Puka
Emel Şimşek
aykut-bozkurt
Onur Tirtir
Burak Velioglu
Jelte Fennema
Ahmet Gedemenli
SaitTalhaNisanci
Onder Kalaci