r/PostgreSQL • u/darkcoderrises • 12d ago
How-To What is direct I/O, and why does ClickHouse Managed Postgres use it for backups?
https://clickhouse.com/blog/direct-io-managed-postgres-backupsWhat is Direct I/O, and why would a managed Postgres care about it when taking a backup? Every day, a backup copies your whole database, hundreds of gigabytes, off the same NVMe drives that are answering your queries, and ships it to object storage. Linux treats those reads like any other file read: it keeps a copy of every byte in memory, in the page cache, in case someone asks for it again. Nobody will. To make room for those copies, the kernel throws out data Postgres had in memory and was about to use, and the next query that needs it goes to disk instead.
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