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## Problem In test environments, the `syncfs` that the pageserver does on startup can take a long time, as other tests running concurrently might have many gigabytes of dirty pages. ## Summary of changes - Add a `no_sync` option to the pageserver's config. - Skip syncfs on startup if this is set - A subsequent PR (https://github.com/neondatabase/neon/pull/9678) will enable this by default in tests. We need to wait until after the next release to avoid breaking compat tests, which would fail if we set no_sync & use an old pageserver binary. Q: Why is this a different mechanism than safekeeper, which as a --no-sync CLI? A: Because the way we manage pageservers in neon_local depends on the pageserver.toml containing the full configuration, whereas safekeepers have a config file which is neon-local-specific and can drive a CLI flag. Q: Why is the option no_sync rather than sync? A: For boolean configs with a dangerous value, it's preferable to make "false" the safe option, so that any downstream future config tooling that might have a "booleans are false by default" behavior (e.g. golang structs) is safe by default. Q: Why only skip the syncfs, and not all fsyncs? A: Skipping all fsyncs would require more code changes, and the most acute problem isn't fsyncs themselves (these just slow down a running test), it's the syncfs (which makes a pageserver startup slow as a result of _other_ tests)