files partitions: no deadlock, four ahead, and a failure no longer stops the GC sweep

Creating a partition deadlocked with file inserts 11 times in an hour, and
each failure ended the GC sweep before its deletes. The parent is now
locked first (lock_timeout 10 s), four partitions are kept ahead, and an
error is logged while the sweep goes on.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/services/FilePartitions.ts

@@ -3,13 +3,16 @@ import logger from '@adonisjs/core/services/logger'
 
 /** Ids per partition (as the migration that partitioned files: …150). */
 export const FILE_PARTITION_SIZE = 4_000_000
-/** Ids kept covered beyond the newest file: two partitions. */
-const AHEAD = 2 * FILE_PARTITION_SIZE
+/**
+ * Ids kept covered beyond the newest file: four partitions (16M ids, about a day of
+ * seeding), so a few sweeps that can't create one are harmless.
+ */
+const AHEAD = 4 * FILE_PARTITION_SIZE
 
 /**
  * `files` is partitioned by id (CONCEPT.md D39). An insert with an id no
  * partition covers fails, so gc:scheduler calls ensure() every sweep to keep
- * two partitions ready ahead of the newest id. Each new partition gets its
+ * four partitions ready ahead of the newest id. Each new partition gets its
  * own unique index on file_key (FileStore.insert checks the older ones),
  * in the parent's tablespace (the HDD on homelab).
  */
@@ -17,8 +20,9 @@ class FilePartitions {
   async ensure(): Promise<string[]> {
     const created: string[] = []
     while (true) {
+      // The sequence, not max(id): cheaper, and it counts ids handed out but not committed yet.
       const { rows } = await db.rawQuery(
-        `SELECT (SELECT coalesce(max(id), 0) FROM files) AS max_id,
+        `SELECT (SELECT last_value FROM files_id_seq) AS max_id,
                 -- ''{0,1}, not ''?: knex reads ? as a binding.
                 max((regexp_match(pg_get_expr(c.relpartbound, c.oid), 'TO \\(''{0,1}(\\d+)''{0,1}\\)'))[1]::bigint) AS upper
          FROM pg_inherits i JOIN pg_class c ON c.oid = i.inhrelid
@@ -28,8 +32,15 @@ class FilePartitions {
       const upper = Number(rows[0].upper)
       if (upper - maxId >= AHEAD) return created
       const name = `files_p${upper}`
-      await db.rawQuery(`CREATE TABLE ${name} PARTITION OF files FOR VALUES FROM (${upper}) TO (${upper + FILE_PARTITION_SIZE})`)
-      await db.rawQuery(`ALTER TABLE ${name} ADD CONSTRAINT ${name}_file_key_unique UNIQUE (file_key)`)
+      // CREATE … PARTITION OF locks files and its partitions one by one, which deadlocked with
+      // file inserts (11 failed sweeps on 2026-10-07). Taking the parent's lock first, in one
+      // statement, can only wait; after 10 s it gives up until the next sweep.
+      await db.transaction(async (trx) => {
+        await trx.rawQuery(`SET LOCAL lock_timeout = '10s'`)
+        await trx.rawQuery(`LOCK TABLE files IN ACCESS EXCLUSIVE MODE`)
+        await trx.rawQuery(`CREATE TABLE ${name} PARTITION OF files FOR VALUES FROM (${upper}) TO (${upper + FILE_PARTITION_SIZE})`)
+        await trx.rawQuery(`ALTER TABLE ${name} ADD CONSTRAINT ${name}_file_key_unique UNIQUE (file_key)`)
+      })
       logger.info(`files: partition ${name} created (ids ${upper}–${upper + FILE_PARTITION_SIZE - 1}).`)
       created.push(name)
     }