Optimize sys.indexes index_id computation for correlated subquery access#4849
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RuchaSK1 wants to merge 4 commits into
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Optimize sys.indexes index_id computation for correlated subquery access#4849RuchaSK1 wants to merge 4 commits into
RuchaSK1 wants to merge 4 commits into
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added 4 commits
June 3, 2026 19:13
Signed-off-by: Rucha Kulkarni <ruchask@amazon.com>
Signed-off-by: Rucha Kulkarni <ruchask@amazon.com>
Signed-off-by: Rucha Kulkarni <ruchask@amazon.com>
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Description
sys.indexescomputesindex_idusing a materialized CTE withrow_number(). TheMATERIALIZEDkeyword forces PostgreSQL to evaluate all indexes in the database upfront, regardless of how many are actually needed by the caller.This is efficient for bulk access (
SELECT * FROM sys.indexes) but becomes a bottleneck whensys.indexesis accessed per-row in correlated subqueries which is a pattern in SSMS Expanding tables query.In such cases, the full CTE is scanned repeatedly (once per outer row), leading to execution times that grow linearly with both the number of tables and total indexes in the database.
Fix
We replace the materialized CTE with an inline scalar subquery that computes
index_idon demand by counting sibling indexes viapg_index_indrelid_index:index_id = 12 + count of earlier non-clustered indexes on the same tableFor per-row access, this reads only the 1-2 sibling indexes on the same table.
Performance Testing
Tested on 17.10 instance with ~37K objects (7,500 tables, 15,751 indexes).
SELECT t.name, i.name FROM sys.tables t JOIN sys.indexes i ON t.object_id = i.object_id AND i.index_id = 1 WHERE t.is_ms_shipped = 0SELECT t.name, i.name, i.index_id FROM sys.tables t JOIN sys.indexes i ON t.object_id = i.object_id WHERE t.is_ms_shipped = 0(all indexes per table)SELECT * FROM sys.indexes(bulk, all 15751 indexes)Issues Resolved
Task: BABEL-6816
Authored-by: Rucha Kulkarni ruchask@amazon.com
Signed-off-by: Rucha Kulkarni ruchask@amazon.com
Test Scenarios Covered
Use case based -
Boundary conditions -
Arbitrary inputs -
Negative test cases -
Minor version upgrade tests -
Major version upgrade tests -
Performance tests - Yes
Tooling impact -
Client tests -
Check List
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