perf: index agent paths so the merged listing and owner counts skip other resources

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vo7HXMdgqXJhR7p8YyVgjB

backend/migrations/20261009173546_agent_owner_prefix_index.down.sql

@@ -0,0 +1 @@
+DROP INDEX IF EXISTS idx_resource_agent_owner_prefix;

backend/migrations/20261009173546_agent_owner_prefix_index.up.sql

@@ -0,0 +1,7 @@
+-- Backs the agent branch of /runnables/list and /runnables/counts, which reach the
+-- `ai_agent` rows of `resource` by workspace and byte-ordered path prefix. Partial, so
+-- neither walks the workspace's other resources (state, cache, ...).
+-- Created CONCURRENTLY via the OVERRIDDEN_MIGRATIONS rewrite in windmill-api/src/db.rs.
+CREATE INDEX IF NOT EXISTS idx_resource_agent_owner_prefix
+    ON resource (workspace_id, path text_pattern_ops)
+    WHERE resource_type = 'ai_agent';

backend/windmill-api/src/db.rs

@@ -111,6 +111,9 @@ lazy_static::lazy_static! {
                     (20260909163047, include_str!(
                         "../../migrations/20260909163047_workspace_delete_cascade_indexes.up.sql"
                     ).replace("CREATE INDEX", "CREATE INDEX CONCURRENTLY").replace("DROP INDEX", "DROP INDEX CONCURRENTLY")),
+                    (20261009173546, include_str!(
+                        "../../migrations/20261009173546_agent_owner_prefix_index.up.sql"
+                    ).replace("CREATE INDEX", "CREATE INDEX CONCURRENTLY")),
                     ].into_iter().collect();
 }
 

backend/windmill-api/src/runnables.rs

@@ -16,7 +16,8 @@
 //! Efficiency: each kind is a UNION ALL branch ordered by an index on
 //! `(workspace_id, archived, <sort key>)` (created_at / edited_at, or the lowered
 //! summary-or-path expression for name orders); Postgres merges the ordered
-//! branches and stops at the page limit. Pagination is keyset — a
+//! branches and stops at the page limit. Agents, which are few, are instead
+//! reached through the partial `idx_resource_agent_owner_prefix` and sorted whole. Pagination is keyset — a
 //! `(sort_key, path, kind, tiebreak)` cursor, where `tiebreak` (a script's hash,
 //! 0 for flow/app) is a stable final key that keeps the order total even when rows
 //! tie on (sort_key, path, kind) — so deep pages don't re-scan. Visibility is
@@ -858,7 +859,7 @@ struct OwnerCount {
 /// `owner/<rest>` is >= `owner || '/'` and, since '/' (0x2F) is immediately
 /// followed by '0' (0x30), < `owner || '0'`. `~>=~` / `~<~` are the
 /// text_pattern_ops operators, which is what lets `idx_<kind>_owner_prefix`
-/// answer the count with an index-only scan — the default opclass sorts by the
+/// (`idx_resource_agent_owner_prefix` for agents) answer the count with an index-only scan — the default opclass sorts by the
 /// database collation and cannot serve a byte-prefix range.
 fn owner_prefix_range(alias: &str) -> String {
     format!("{alias}.path ~>=~ (o.owner || '/') AND {alias}.path ~<~ (o.owner || '0')")