Track cluster-wide Citus version - method 3 - (shmem cache + daemon invalidate) - #8690
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alperkocatas wants to merge 1 commit into
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Track cluster-wide Citus version - method 3 - (shmem cache + daemon invalidate)#8690alperkocatas wants to merge 1 commit into
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…dation) Add citus_version_num() and citus_minimum_cluster_version() backed by a node-local shared-memory cache. The cache is invalidated from the pg_dist_node relcache callback and periodically by the maintenance daemon (citus.cluster_version_refresh_interval) so the next read recomputes. The daemon task only flips a flag: no transaction, lock, or fan-out. No catalog changes.
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Pull request overview
Adds cluster-wide Citus version introspection by introducing a node-local shared-memory cache for the computed minimum Citus version across active primary nodes, with invalidation triggered by pg_dist_node relcache events and periodically by the maintenance daemon.
Changes:
- Add
pg_catalog.citus_version_num()(integer-encoded Citus version) and SQL wiring. - Add
pg_catalog.citus_minimum_cluster_version()backed by a shared-memory cache and remote fan-out computation on cache miss. - Add cache invalidation hooks (relcache callback + maintenance daemon) and a new GUC
citus.cluster_version_refresh_interval.
Reviewed changes
Copilot reviewed 12 out of 12 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
| src/include/distributed/cluster_version.h | Declares cluster version cache APIs and refresh-interval GUC. |
| src/backend/distributed/utils/maintenanced.c | Adds periodic invalidation of the cluster version cache. |
| src/backend/distributed/utils/citus_version.c | Exposes new citus_version_num() C UDF. |
| src/backend/distributed/sql/udfs/citus_version_num/latest.sql | Creates pg_catalog.citus_version_num() for new installs. |
| src/backend/distributed/sql/udfs/citus_version_num/15.0-1.sql | Creates pg_catalog.citus_version_num() for 15.0-1 upgrade path. |
| src/backend/distributed/sql/udfs/citus_minimum_cluster_version/latest.sql | Creates pg_catalog.citus_minimum_cluster_version() for new installs. |
| src/backend/distributed/sql/udfs/citus_minimum_cluster_version/15.0-1.sql | Creates pg_catalog.citus_minimum_cluster_version() for 15.0-1 upgrade path. |
| src/backend/distributed/sql/downgrades/citus--15.0-1--14.0-1.sql | Drops the newly added version-tracking UDFs on downgrade. |
| src/backend/distributed/sql/citus--14.0-1--15.0-1.sql | Includes the new UDF SQL files in the 14→15 upgrade script. |
| src/backend/distributed/shared_library_init.c | Requests shmem + installs init hook + registers the refresh-interval GUC. |
| src/backend/distributed/operations/cluster_version.c | Implements shmem cache, minimum version computation, and invalidation. |
| src/backend/distributed/metadata/metadata_cache.c | Invalidates the version cache when pg_dist_node changes. |
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| /* | ||
| * InvalidateClusterVersionCache marks the cached minimum version as stale so | ||
| * that the next reader recomputes it. It is called from the pg_dist_node | ||
| * relcache invalidation callback. We intentionally do not take the LWLock here, | ||
| * matching InvalidateNodeRelationCacheCallback, to keep the callback safe and | ||
| * cheap; a racy stale read only costs one extra recompute. | ||
| */ | ||
| void | ||
| InvalidateClusterVersionCache(void) | ||
| { | ||
| if (ClusterVersionShmem != NULL) | ||
| { | ||
| ClusterVersionShmem->cacheValid = false; | ||
| } | ||
| } |
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| CREATE OR REPLACE FUNCTION pg_catalog.citus_minimum_cluster_version() | ||
| RETURNS text | ||
| LANGUAGE C STRICT | ||
| AS 'MODULE_PATHNAME', $$citus_minimum_cluster_version$$; |
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| CREATE OR REPLACE FUNCTION pg_catalog.citus_minimum_cluster_version() | ||
| RETURNS text | ||
| LANGUAGE C STRICT | ||
| AS 'MODULE_PATHNAME', $$citus_minimum_cluster_version$$; |
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Add citus_version_num() and citus_minimum_cluster_version() backed by a node-local shared-memory cache. The cache is invalidated from the pg_dist_node relcache callback and periodically by the maintenance daemon (citus.cluster_version_refresh_interval) so the next read recomputes. The daemon task only flips a flag: no transaction, lock, or fan-out. No catalog changes.
Downside is: daemon will invalidate cache even if no change has occurred in the cluster since last recompute of minimum version.
DESCRIPTION: PR description that will go into the change log, up to 78 characters