fix: index slot recovery lookups by LSN

[psteinroe]

add a partitioned BRIN index on pgstream.events(lsn) so invalidated-slot recovery is fast.

chose brin because writes are cheap, lsns closely follow physical row order and in most recovery scenarios the filtered set is small enough for a cheap top-n sort by (created_at, id).

Production rollout

run the following script before deploying the new version. do not wrap it in a transaction.

\set ON_ERROR_STOP on-- A valid parent means this rollout already completed.SELECT coalesce((
SELECTindex_metadata.indisvalidFROM pg_index AS index_metadata
WHEREindex_metadata.indexrelid= to_regclass('pgstream.events_lsn_brin_idx')
), false) AS rollout_complete
\gset
\if :rollout_complete
\echo 'pgstream.events_lsn_brin_idx is already valid; nothing to do.'
\else
SELECT pg_advisory_lock(hashtext('pgstream.events_lsn_brin_idx'));
-- Remove invalid standalone indexes left by an interrupted build.SELECT format('DROP INDEX CONCURRENTLY %I.%I;', namespace.nspname, child_index.relname)
FROM pg_partition_tree('pgstream.events'::regclass) AS partition_tree
JOIN pg_class AS partition ONpartition.oid=partition_tree.relidJOIN pg_namespace AS namespace ONnamespace.oid=partition.relnamespaceJOIN pg_class AS child_index
ONchild_index.relnamespace=namespace.oidANDchild_index.relname=partition.relname||'_lsn_brin_idx'JOIN pg_index AS child_metadata ONchild_metadata.indexrelid=child_index.oidWHEREpartition_tree.isleafANDchild_metadata.indrelid=partition.oidAND NOT child_metadata.indisvalidAND NOT EXISTS (
SELECT1FROM pg_inherits WHERE inhrelid =child_index.oid
)
ORDER BYpartition.relname
\gexec
-- Build one leaf index at a time without blocking writes.SELECT format(
'CREATE INDEX CONCURRENTLY %I ON %I.%I USING brin (lsn) WITH (pages_per_range = 64, autosummarize = on);',
partition.relname||'_lsn_brin_idx', namespace.nspname, partition.relname
)
FROM pg_partition_tree('pgstream.events'::regclass) AS partition_tree
JOIN pg_class AS partition ONpartition.oid=partition_tree.relidJOIN pg_namespace AS namespace ONnamespace.oid=partition.relnamespaceLEFT JOIN pg_class AS expected_index
ONexpected_index.relnamespace=namespace.oidANDexpected_index.relname=partition.relname||'_lsn_brin_idx'WHEREpartition_tree.isleafANDexpected_index.oid IS NULLAND NOT EXISTS (
SELECT1FROM pg_inherits AS attachment
JOIN pg_index AS inherited_index ONinherited_index.indexrelid=attachment.inhrelidWHEREattachment.inhparent= to_regclass('pgstream.events_lsn_brin_idx')
ANDinherited_index.indrelid=partition.oid
)
ORDER BYpartition.relname
\gexec
-- Create only the parent metadata, then attach the concurrently-built children.SET lock_timeout ='5s';
CREATEINDEXIF NOT EXISTS events_lsn_brin_idx
ON ONLY pgstream.events
USING brin (lsn)
WITH (pages_per_range =64, autosummarize =on);
SELECT format(
'ALTER INDEX pgstream.events_lsn_brin_idx ATTACH PARTITION %I.%I;',
namespace.nspname, child_index.relname
)
FROM pg_partition_tree('pgstream.events'::regclass) AS partition_tree
JOIN pg_class AS partition ONpartition.oid=partition_tree.relidJOIN pg_namespace AS namespace ONnamespace.oid=partition.relnamespaceJOIN pg_class AS child_index
ONchild_index.relnamespace=namespace.oidANDchild_index.relname=partition.relname||'_lsn_brin_idx'JOIN pg_index AS child_metadata ONchild_metadata.indexrelid=child_index.oidWHEREpartition_tree.isleafANDchild_metadata.indrelid=partition.oidANDchild_metadata.indisreadyANDchild_metadata.indisvalidAND NOT EXISTS (
SELECT1FROM pg_inherits AS attachment
JOIN pg_index AS inherited_index ONinherited_index.indexrelid=attachment.inhrelidWHEREattachment.inhparent='pgstream.events_lsn_brin_idx'::regclass
ANDinherited_index.indrelid=partition.oid
)
ORDER BYpartition.relname
\gexec
RESET lock_timeout;
DO $$
BEGIN
IF NOT EXISTS (
SELECT1FROM pg_index
WHERE indexrelid ='pgstream.events_lsn_brin_idx'::regclass
AND indisready
AND indisvalid
) THEN
RAISE EXCEPTION 'pgstream.events_lsn_brin_idx is not valid; rerun the rollout before deploying';
END IF;
END
$$;
SELECT pg_advisory_unlock(hashtext('pgstream.events_lsn_brin_idx'));
\endif