The chat_history query
WHERE workspace_id = $1
AND activity_type = 'a2a_receive'
AND (source_id = $2 OR target_id = $2)
ORDER BY created_at DESC
forces a workspace-scoped seq-scan-and-filter at every call —
idx_activity_ws_type_time covers workspace_id+type prefix but the
(source OR target) clause then walks every workspace row. Demo
workspaces (≤50 rows) don't notice; production workspaces accumulate
thousands over months and chat_history latency grows linearly.
Adds two partial btree indexes (workspace_id, source_id) WHERE NOT NULL
and (workspace_id, target_id) WHERE NOT NULL. Postgres BitmapOrs them
into a workspace-scoped BitmapAnd against the existing index, dropping
chat_history from O(workspace_rows) to O(peer_a2a_rows).
Partial WHERE NOT NULL because most activity rows (heartbeats,
agent_log, memory_write, etc.) carry NULL source_id/target_id and
shouldn't bloat the index.
Anti-pattern caveat (per the issue): a single compound (a, b) index
can't serve 'a OR b' — Postgres only uses compound for prefix match.
Two separate indexes + BitmapOr is the right shape.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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