When does memory spike during BGSAVE?
If the parent process rewrites a large fraction of the dataset while the child is dumping, the OS must copy many pages. A 50% rewrite of an 8 GB heap can require 4 GB of new physical memory.
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Copy-on-Write Snapshotsfork() shares parent memory, copying only written pages for non-blocking snapshots. Write-heavy loads can spike memory to 2x under load.
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