docs: parallel WAL writes and delta shipping to replicas - #1746
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Document the new commit path on MAIN: the deltas of a transaction are encoded for every replica in parallel with MAIN's own WAL write, instead of the WAL write and each replica running in turn. - how-replication-works: new "Parallel WAL writes and delta shipping" section covering the durability gate, preserved per-replica ordering and WAL order, and per-replica failure containment; note that both 2PC phases fan out across STRICT_SYNC replicas; correct the ASYNC section, which claimed one background thread per replica. - best-practices: MAIN keeps two background threads per registered replica, so leave CPU headroom when registering many. - release-notes: v3.13.0 improvement entry for memgraph#4645.
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September 2, 2026 05:43
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Release note
Commits on a MAIN instance with replicas are faster: MAIN now encodes a
transaction for every replica in parallel with writing its own WAL, instead of
doing the WAL write and each replica in turn. Commit latency no longer grows
linearly with the number of registered replicas. Durability still gates
replication — a replica only receives the transaction end after MAIN's WAL write
succeeded — and per-replica ordering, WAL order, and the reported SYNC /
STRICT_SYNC failures are unchanged. Each replica also gets a separate background
worker for state checks and recovery, so a long recovery no longer delays
replication of new transactions.
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