Write throughput · 16 writes — sequential append (LSM) vs random in-place update (B-tree)
LSM-tree · append to end of log0 disk-cost
B-tree · seek to a random page, rewrite it0 disk-cost
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Volatile Memory RAM
Lost on crash — which is why each write hits the WAL on disk first. On restart the WAL is replayed to rebuild this table.
Durable Storage disk · survives crashes
Write-Ahead Log · append-only
SSTable Levels each carries a Bloom filter
MemTable / found
WAL / Bloom bit
SSTable read
compaction
tombstone / skip