9:41
Write Path Trade-offs B-Tree Buffer pool keys 1–64 keys 65–128 1–32 33–64 65–96 97–128 • Updates land in place • Point reads in O(log n) • Write amplification ~4.6x LSM Tree Memtable flush L0 L1 L2 L3 L4 sst-0041 · 12 MB sst-0038 · 96 MB sst-0022 · 740 MB • Writes stay sequential • Merge cost paid on read • Compaction runs nightly Write-Ahead Log Log head segment 0142 segment 0143 • Durable before the ack returns • Replayed from the last checkpoint • Truncated once L0 is flushed
Backpressure Feb 18, 2026

Write Paths: B-Trees, LSM Trees, and the Log

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