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If it's enabled, WAL archive segments that are older than 1 checkpoint in past (they are no longer needed for crash recovery) will be filtered from physical records and compressed to ZIP format. In case of demand (e.g. delta-rebalancing in case of topology change), they will be uncompressed back to RAW format. Experiments show that factor between compacted and RAW segments is 10x on usual data and 3x in worst case (secure random data in updates).
Please note that as long as ZIP segments don't contain any data needed for crash recovery, they can be deleted anytime in case of need for disk space (it will affect rebalancing though).

Setting input-output

I/O abstraction determines how disk features are accessed by native persistence.

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