perf(sqlite): bulk-ingest write-path defaults — 64 MiB page cache + 50k WAL autocheckpoint

crates/persistence/src/backends/sqlite/backend.rs

@@ -327,6 +327,25 @@ impl SqliteBackend {
             if enable_foreign_keys {
                 conn.execute_batch("PRAGMA foreign_keys = ON;")?;
             }
+            // 64 MiB page cache (negative = KiB). SQLite's 2 MiB default
+            // thrashes once the search_index B-trees outgrow it: during a
+            // bulk import every index INSERT and batch commit evicts and
+            // rewrites hot pages. Measured on a real 31 GB import, raising it
+            // took ingest from 232/s to 289/s (+25%), cutting index-row
+            // INSERT cost 1.71→1.24 ms and commit cost 1.95→1.72 ms per
+            // entry. The limit is per pooled connection (pool of 10), but
+            // only connections that touch that many pages grow their cache.
+            conn.execute_batch("PRAGMA cache_size = -65536;")?;
+            // Checkpoint every ~50,000 WAL pages (~200 MiB) instead of every
+            // 1,000 (~4 MiB). A bulk-ingest batch writes far more than 4 MiB
+            // of WAL, so with the default every batch commit also ran a
+            // checkpoint and paid the WAL->database copy inline; fewer,
+            // larger checkpoints move the same bytes sequentially. Measured
+            // stepwise on the same real-manifest window: 10,000 pages took
+            // 289/s -> 382/s (commit 1.72 -> 0.96 ms per entry) and 50,000
+            // took 417/s -> 501/s on the multi-row branch (commit -> 0.55 ms).
+            // Cost: the -wal file grows to ~200 MiB under sustained writes.
+            conn.execute_batch("PRAGMA wal_autocheckpoint = 50000;")?;
             crate::sof::sqlite_udfs::register(conn).map_err(|e| {
                 rusqlite::Error::SqliteFailure(
                     rusqlite::ffi::Error::new(rusqlite::ffi::SQLITE_ERROR),