fix(trigger): exclude constraint indexes from critical severity - #44
randoneering merged 2 commits into
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📝 WalkthroughWalkthroughThe large-index health checks now distinguish ordinary unread indexes from indexes that support unique or exclusion constraints. Critical checks report only non-constraint indexes. Separate medium-severity checks report large unread constraint-backed indexes and recommend reviewing the underlying constraint. The function and both views use this classification. Merge Risk: 🔵 Low · up to Large standalone unique indexes may be downgraded and advised to review a constraint that does not exist, reducing the accuracy of unused-index remediation. Update the classification to identify actual constraint-backed indexes before merge. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Before this commit, any large (> 100 MB) index with 0 scans was considered unused with a diagnostic severity of CRITICAL. Some indexes are never intended to be read, but instead only used for enforcing uniqueness or foreign key constraints. It is misleading to label the lack of scans of these indexes as a CRITICAL error. This commit - keeps the CRITICAL severity diagnostic for un-scanned indexes that are not used in constraints, but - demotes the severity of un-scanned unique/FK/exclusion constraint indexes to MEDIUM, and clarifies that the recommended action for them might be different than for access-serving indexes. (Note that exclusion indexes do actually trigger a scan and increment idx_scan, but this seems more like an implementation detail and not a reliable requirement on exclusion indexes, so they are still covered by this change.) The reason for the low severity level for these constraint-backing indexes is that it seems highly probable they are there for a reason. If a constraint-backing index is incorrect, then that is very likely to have been discovered by the time it has grown large, because then many expected-to-succeed inserts would have failed due to violation of the constraint. There's also no way from within the database to tell whether the constraint is still relevant or not. The combination of high risk of false positive with low risk of false negative means a low severity level is appropriate. This also makes the name "Unused Large Index" of the pre-existing check more accurate, because previously it said "unused" even though it may have been used to enforce constraints (it was merely "un-scanned"). Now that name is correct – an access-serving index that is unread truly appears unused as far as can be told from within the database.
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PR Summary by QodoDemote unread constraint indexes from critical severity
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Code Review by Qodo
1. Standalone unique indexes get bad advice
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In `@pgFirstAid.sql`:
- Around line 408-409: Replace the indisunique-only filtering in both query
sites with an explicit pg_constraint ownership check using pgi.indexrelid, so
standalone unique indexes are excluded from constraint-only guidance. Apply the
same correction at pgFirstAid.sql lines 408-409 and 433-434, view_pgFirstAid.sql
lines 397-398 and 419-420, and view_pgFirstAid_managed.sql lines 392-393 and
414-415; retain the existing exclusion handling for non-unique and exclusion
indexes.
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@kqr thanks for the PR! I am going to take a look sometime today and review what the coding agent's have pointed out (to see if they are valid). |
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Before this commit, any large (> 100 MB) index with 0 scans was considered unused with a diagnostic severity of CRITICAL. Some indexes are never intended to be read, but instead only used for enforcing uniqueness or foreign key constraints. It is misleading to label the lack of scans of these indexes as a CRITICAL error.
This commit
keeps the CRITICAL severity diagnostic for un-scanned indexes that are not used in constraints, but
demotes the severity of un-scanned unique/FK/exclusion constraint indexes to MEDIUM, and clarifies that the recommended action for them might be different than for access-serving indexes. (Note that exclusion indexes do actually trigger a scan and increment idx_scan, but this seems more like an implementation detail and not a reliable requirement on exclusion indexes, so they are still covered by this change.)
The reason for the low severity level for these constraint-backing indexes is that it seems highly probable they are there for a reason. If a constraint-backing index is incorrect, then that is very likely to have been discovered by the time it has grown large, because then many expected-to-succeed inserts would have failed due to violation of the constraint. There's also no way from within the database to tell whether the constraint is still relevant or not. The combination of high risk of false positive with low risk of false negative means a low severity level is appropriate.
This also makes the name "Unused Large Index" of the pre-existing check more accurate, because previously it said "unused" even though it may have been used to enforce constraints (it was merely "un-scanned"). Now that name is correct – an access-serving index that is unread truly appears unused as far as can be told from within the database.
Pull Request Summary
Type of Change
Related Issues
Testing
PostgreSQL Version Compatibility
Has this code been tested against the following PostgreSQL versions?
Testing notes:
Managed Database Platforms
Has this code been deployed and tested on the following platforms?
Platform-specific notes:
Additional Notes
Updated the unused large-index diagnostic to keep non-constraint indexes at CRITICAL and report unused unique or exclusion constraint indexes at MEDIUM. Clarified the guidance and check names to distinguish access-serving indexes from constraint-supporting indexes.