caching: adaptive append-only lease reset capacity hint

[snissn]

Summary

• add a bounded/decayed appendOnlyEntryHint from observed append-only mutable sizes at shard rotation
• apply the hint only to append-only lease/recycle hard resets (ResetWithCapacityHard) so retained memtables do not keep oversized entry slices after spikes
• keep active mutable creation sizing unchanged (avoids the regrowth churn regression)
• export hint telemetry in stats:
  • treedb.cache.append_only.entry_hint_entries
  • treedb.cache.append_only.entry_hint_capacity_bytes
  • process mirrors
• add focused tests in TreeDB/caching/append_only_hint_test.go

Validation

• go test ./TreeDB/caching -count=1
• go test ./TreeDB/internal/memtable -count=1
• go test ./TreeDB/db -run TestDoesNotExist -count=1
• go vet ./TreeDB/caching

Unified Bench (serial, same args)

Candidate profile dir: /home/mikers/tmp/perf-append-hint-v2-1773568813
Baseline profile dir: /home/mikers/tmp/perf-append-hint-base-1773568648

Throughput deltas (TreeDB):

• sequential_write: +12.59%
• random_write: -4.58%
• dataset_write_random: -4.64%
• batch_write: +5.05%
• batch_write_steady: +1.95%
• random_read: -0.40%

Alloc-space deltas (TreeDB):

• sequential_write total: 199.24MB -> 138.21MB (-30.63%)
• random_write total: 30,410.35kB -> 24,557.59kB (-19.25%)
• batch_write_steady total: 155.64MB -> 141.77MB (-8.91%)

Celestia runs (this branch)

fast:

• /home/mikers/.celestia-app-mainnet-treedb-20260315000234
  • duration_seconds=303
  • max_rss_kb=11869152
  • end_app_bytes=4745471322
• /home/mikers/.celestia-app-mainnet-treedb-20260315001415
  • duration_seconds=293
  • max_rss_kb=10193048
  • end_app_bytes=4813039808

wal_on_fast:

• /home/mikers/.celestia-app-mainnet-treedb-20260315000807
  • duration_seconds=336
  • max_rss_kb=10134740
  • end_app_bytes=4686263016
• /home/mikers/.celestia-app-mainnet-treedb-20260315001936
  • duration_seconds=349
  • max_rss_kb=11439180
  • end_app_bytes=4876966298

Notes:

• no correctness failures in these runs
• fast RSS signal is noisier across replicates; wal_on_fast shows lower RSS than recent caching: export vlog mmap telemetry via expvar #830 baseline samples while preserving completion and similar disk footprint

[Copilot]

Pull request overview

This PR adds an adaptive sizing hint for append-only memtable hard resets (lease recycle/trim) based on recently observed mutable sizes at shard rotation, aiming to avoid retaining oversized entry slices after workload spikes while keeping active mutable sizing unchanged.

Changes:

• Track a bounded/decayed appendOnlyEntryHint from observed append-only mutable entry counts during shard rotation.
• Apply the hint only when calling ResetWithCapacityHard for append-only memtables during recycle/lease trimming.
• Export the hint in DB.Stats() and add focused unit tests for decay/clamping and overflow behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
TreeDB/caching/db.go	Adds adaptive append-only entry hint tracking, applies it to append-only hard resets, and exports hint telemetry via Stats().
TreeDB/caching/append_only_hint_test.go	Adds tests covering hint decay/clamping and overflow-safe capacity computation.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 1e861bf791

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

[Copilot]

Pull request overview

This PR introduces an adaptive, bounded “append-only entry hint” in caching.DB to better size append-only memtable hard resets (lease/pool recycle paths) based on recently observed mutable shard sizes, reducing post-spike retained entry-slice over-allocation while keeping active mutable sizing unchanged.

Changes:

• Track a decayed/clamped appendOnlyEntryHint (observed at mutable shard rotation) and use it to compute an effective capacity for append-only ResetWithCapacityHard paths.
• Export the hint as stats under both treedb.cache.append_only.* and treedb.process.append_only.*.
• Add focused unit tests covering decay/clamping and overflow safety.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
TreeDB/caching/db.go	Adds append-only hint tracking, applies hinted capacity to append-only hard resets, and exports hint telemetry in Stats().
TreeDB/caching/append_only_hint_test.go	Adds tests for hint decay/clamping behavior and overflow-safe capacity derivation.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[Copilot]

Pull request overview

Adds an adaptive (bounded + decayed) append-only entry slice sizing hint derived from observed append-only mutable sizes at shard rotation, and applies it only when hard-resetting/recycling append-only memtables to avoid retaining oversized entry slices after spikes.

Changes:

• Track an appendOnlyEntryHint on DB, updated on append-only shard rotation using a grow/decay filter.
• Apply the hint when calling ResetWithCapacityHard for append-only memtables during recycle/lease trimming.
• Export hint telemetry via cache/process stats and add focused tests for decay/clamping and overflow safety.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
TreeDB/caching/db.go	Implements the adaptive hint, applies it to append-only hard resets, and exports stats telemetry.
TreeDB/caching/append_only_hint_test.go	Adds tests validating hint decay/clamping behavior and overflow-safe capacity conversion.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.

[Copilot]

Pull request overview

This PR introduces an adaptive, bounded, and decaying appendOnlyEntryHint in the caching DB to better size recycled/leased append-only memtables after transient spikes, aiming to reduce retained entry-slice memory while avoiding churn in active mutable sizing.

Changes:

• Track an adaptive appendOnlyEntryHint based on observed append-only mutable entry counts at shard rotation.
• Apply the hint when performing append-only lease/recycle hard resets (ResetWithCapacityHard) to cap retained capacity after spikes.
• Export hint telemetry via new treedb.cache.* and treedb.process.* stats keys, and add focused unit tests for the hint logic.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
TreeDB/caching/db.go	Adds adaptive hint tracking, applies it to append-only hard-reset capacity during recycling/lease trimming, and exports new stats.
TreeDB/caching/append_only_hint_test.go	Adds unit tests validating hint decay behavior and overflow-safe capacity conversion.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

You can also share your feedback on Copilot code review. Take the survey.