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SQLITE_OPTIMIZATIONS.md

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SQLite Optimizations

Brief tracker for SQLite cold-read, VFS, and storage performance work.

Current baseline: .agent/notes/sqlite-cold-read-before.txt records a 50 MiB cold full-scan read at 20.14s e2e, 1,249 VFS get_pages calls, and 19.33s VFS transport.

Implementation tracking lives in scripts/ralph/prd.json.

Range page-read protocol details live in .agent/specs/sqlite-range-page-read-protocol.md.

Existing Optimizations

  • Actor startup can preload SQLite VFS pages through OpenConfig.preload_pgnos, OpenConfig.preload_ranges, and persisted /PRELOAD_HINTS; first pages, hint mechanisms, and the preload byte budget are configured through central SQLite optimization flags.
  • The VFS keeps a short-lived staging cache for startup preload and read-ahead pages. Direct target pages fetched for xRead are not retained in VFS memory.
  • Any speculative page consumed by xRead, including page 1, is evicted from the VFS staging cache after SQLite receives it. Before the first commit, a lazy page-1 read for a missing database synthesizes the empty SQLite header again instead of retaining page bytes. Staged pages that SQLite never reads expire through RIVETKIT_SQLITE_OPT_VFS_STAGING_CACHE_TTL_MS.
  • Commit completion stages dirty pages in a separate TTL cache so SQLite can reread its own writes without turning the VFS into a permanent second pager.
  • VFS staging cache behavior is selected with RIVETKIT_SQLITE_OPT_VFS_PAGE_CACHE_MODE=off|target|startup|prefetch|all, with capacity configured separately. The protected-cache budget no longer pins VFS page bytes beyond xRead.
  • The VFS has speculative read-ahead selected with RIVETKIT_SQLITE_OPT_READ_AHEAD_MODE=off|bounded|adaptive; the default bounded budget is 64 pages, which reduced the cold-read benchmark from 1,249 to 368 VFS get_pages calls.
  • The VFS tracks bounded recent page hints as hot pages plus coalesced scan ranges; NativeDatabase::snapshot_preload_hints() exposes the in-memory plan for future flush wiring.
  • Actor Prometheus metrics expose VFS read counters, fetched bytes, cache hits/misses, and get_pages duration at /gateway/<actor_id>/metrics.
  • sqlite-storage keeps an in-memory PIDX cache and decodes each unique DELTA/SHARD blob once per get_pages(...) call.
  • sqlite-storage exposes get_page_range(...) for bounded contiguous reads; it reuses get_pages(...) source resolution and currently caps ranges at 256 pages / 1 MiB.
  • sqlite-storage reassembles large chunked logical values with one bounded chunk-prefix range read by default; RIVETKIT_SQLITE_OPT_BATCH_CHUNK_READS=false selects serial 10 KB chunk gets for comparison runs.
  • sqlite-storage caches decoded DELTA/SHARD LTX blobs across repeated reads by default, with RIVETKIT_SQLITE_OPT_DECODED_LTX_CACHE=false preserving per-read decode behavior.
  • sqlite-storage compaction folds DELTA pages into SHARD blobs for steadier read behavior.
  • The native read-mode/write-mode SQLite connection manager routes read-only statements to pooled read-only connections and routes writes, transactions, and fallbacks through exclusive write mode. Read-pool v1 closes readers before writes and does not pin per-reader head txids.

Recommended Optimizations

  • Gate SQLite cold-read optimizations behind central env-backed feature flags that default on, so each optimization can be benchmarked on and off.
  • Add adaptive forward-scan read-ahead that can grow beyond shard-sized batches for mostly sequential reads while shrinking back for scattered access.
  • Extend adaptive scan read-ahead to support both forward and backward sequential page access.
  • Record VFS predictor access on cache hits so prefetch learns real sequential scans.
  • Cache repeated pegboard-envoy SQLite actor validation and local-open checks for active actors.
  • Return SQLite meta from sqlite-storage::get_pages(...) instead of doing a second META read in pegboard-envoy.
  • Persist capped VFS preload hints on sleep/close and feed them into OpenConfig on the next actor start.
  • Add a bulk or range page-read protocol so cold scans do not require page-list request loops.
  • Reduce storage read amplification from whole-blob LTX decode further with page-frame-addressable storage.
  • Benchmark compacted and un-compacted cold reads separately.

Preload Hint Policy

  • VFS preload hints are page-number based. SQLite index, table, schema, and overflow pages all hit VFS on pager-cache misses, but SQLite's pager cache can hide repeat access after the first read.
  • Preload selection should consider early-after-wake pages in addition to frequency and scan ranges, because index/root/schema pages may be important even when VFS only observes them once per actor lifetime.
  • Preload hint mechanisms must be independently configurable through the central SQLite optimization feature flag/config file, not scattered std::env reads.
  • Supported preload mechanisms should include first pages, persisted hot pages, early-after-wake pages, and persisted scan ranges.
  • All preload mechanisms should default on only when bounded by OpenConfig.max_total_bytes or an equivalent preload byte budget.

Scan Read-Ahead Notes

  • SQLite B-trees are sorted logically, not guaranteed linearly by page number; append-heavy INTEGER PRIMARY KEY tables are more likely to produce forward page scans than mixed inserts or freelist reuse.
  • INTEGER PRIMARY KEY aliases rowid, so rowid/primary-key range scans are usually the best case for forward or backward VFS read-ahead.
  • Non-integer primary keys on rowid tables use a separate index; index range scans can produce scattered table-page reads unless the index order is correlated with rowid or the query is covered by the index.
  • WITHOUT ROWID tables are keyed by the declared primary key, but page splits can still make logical key order differ from physical page-number order.
  • Adaptive read-ahead should grow only when observed VFS misses are directional, including both increasing and decreasing page numbers, and shrink for scattered access.

Update Rules

  • Add new SQLite read/write performance ideas here before implementation if they change VFS, storage layout, actor startup preload, or metrics.
  • Move completed ideas into "Existing Optimizations" with the measured benchmark delta.
  • Keep benchmark artifacts under .agent/notes/sqlite-cold-read-*.txt.