docs: document ingester WAL truncation mechanics#7661
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Add a dedicated blocks-storage/ingester-wal.md page covering the WAL write path, replay on startup, and — most notably — exactly what triggers WAL truncation: the head-compaction loop, the 1.5 x block-ranges-period head-compactable threshold, the head-compaction-idle-timeout forced path, and the lower-two-thirds checkpoint window inside TSDB's truncateWAL. Cross-link the new page from the blocks-storage overview and from the ingester section of production-tips. Signed-off-by: Charlie Le <charlie_le@apple.com>
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Jul 2, 2026
| | `-blocks-storage.tsdb.head-compaction-idle-timeout` | `1h` | Forces compaction (and therefore truncation) for tenants whose head is not otherwise compactable. `0` disables. | | ||
| | `-blocks-storage.tsdb.block-ranges-period` | `2h` | Sets both the block size and the `3/2 × block-range` head-compactable threshold. | | ||
| | `-blocks-storage.tsdb.wal-compression-type` | *(none)* | `snappy` or `zstd` reduces WAL size on disk; does not change truncation timing. | | ||
| | `-blocks-storage.tsdb.wal-segment-size-bytes` | TSDB default | Changes the size of each WAL segment; does not change truncation timing. | |
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Could we make this default explicit as 134217728 (TSDB default, 128 MiB) instead of just TSDB default?
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Summary
docs/blocks-storage/ingester-wal.md, a dedicated page covering the ingester WAL: write path, replay on startup, and — most notably — exactly what triggers WAL truncation.1.5 × block-ranges-periodhead-compactable threshold, thehead-compaction-idle-timeoutforced-compaction path, and the lower-two-thirds checkpoint window inside TSDB'struncateWAL.docs/blocks-storage/_index.mdand from the Ingester section ofdocs/blocks-storage/production-tips.md.Motivation
The existing docs only state that "the WAL is truncated when a new TSDB block is created, which by default occurs every 2 hours." That is roughly true for busy tenants but leaves several questions unanswered:
head-compaction-idle-timeout.)retention-period)?The new page consolidates that information in one place so operators tuning ingester disk usage don't have to trace through vendored TSDB code.
Test plan
./ingester-wal.md,../guides/ingesters-rolling-updates.md,./production-tips.md#ingester-disk-space.weight: 5,slug: ingester-wal) matches sibling pages underdocs/blocks-storage/.Docs-only change; no code, tests, or config are modified.