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Doc: clarify the conditions of usable indexes for REPLICA IDENTITY FULL tables.

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Commit 89e46da5e allowed REPLICA IDENTITY FULL tables to use an index
on the subscriber during apply of update/delete. This commit clarifies
in the documentation that the leftmost field of candidate indexes must
be a column (not an expression) that references the published relation
column.

The source code comments are also updated accordingly.

Reviewed-by: Peter Smith, Amit Kapila
Discussion: https://postgr.es/m/CAD21AoDJjffEvUFKXT27Q5U8-UU9JHv4rrJ9Ke8Zkc5UPWHLvA@mail.gmail.com
Backpatch-through: 16
This commit is contained in:
Masahiko Sawada
2023-07-13 15:03:17 +09:00
parent 0fef877538
commit fd48a86c62
3 changed files with 13 additions and 16 deletions
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11
src/backend/replication/logical/relation.c
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@ -779,9 +779,10 @@ RemoteRelContainsLeftMostColumnOnIdx(IndexInfo *indexInfo, AttrMap *attrmap)
/*
* Returns the oid of an index that can be used by the apply worker to scan
* the relation. The index must be btree, non-partial, and have at least
* one column reference (i.e. cannot consist of only expressions). These
* limitations help to keep the index scan similar to PK/RI index scans.
* the relation. The index must be btree, non-partial, and the leftmost
* field must be a column (not an expression) that references the remote
* relation column. These limitations help to keep the index scan similar
* to PK/RI index scans.
*
* Note that the limitations of index scans for replica identity full only
* adheres to a subset of the limitations of PK/RI. For example, we support
@ -796,10 +797,6 @@ RemoteRelContainsLeftMostColumnOnIdx(IndexInfo *indexInfo, AttrMap *attrmap)
* none of the tuples satisfy the expression for the index scan, we fall-back
* to sequential execution, which might not be a good idea in some cases.
*
* We also skip indexes if the remote relation does not contain the leftmost
* column of the index. This is because in most such cases sequential scan is
* favorable over index scan.
*
* We expect to call this function when REPLICA IDENTITY FULL is defined for
* the remote relation.
*