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a2a44ea213
Instead of thinking in terms of 'latest' and 'lsn' of the request, each request has two LSNs: the request LSN and 'not_modified_since' LSN. The request is nominally made at the request LSN, that determines what page version we want to see. But as a hint, we also include 'not_modified_since'. It tells the pageserver that the page has not been modified since that LSN, which allows the pageserver to skip waiting for newer WAL to arrive, and could allow more optimizations in the future. Refactor the internal functions to calculate the request LSN to calculate both LSNs. Sending two LSNs to the pageserver requires using the new protocol version 2. The previous commit added the server support for it, but we still default to the old protocol for compatibility with old pageservers. The 'neon.protocol_version' GUC can be used to use the new protocol. The new protocol addresses one cause of issue #6211, although you can still get the same error if you have a standby that is lagging behind so that the page version it needs is genuinely GC'd away.
neon extension consists of several parts:
shared preload library neon.so
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implements storage manager API and network communications with remote page server.
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walproposer: implements broadcast protocol between postgres and WAL safekeepers.
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control plane connector: Captures updates to roles/databases using ProcessUtility_hook and sends them to the control ProcessUtility_hook.
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remote extension server: Request compute_ctl to download extension files.
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file_cache: Local file cache is used to temporary store relations pages in local file system for better performance.
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relsize_cache: Relation size cache for better neon performance.
SQL functions in neon--*.sql
Utility functions to expose neon specific information to user and metrics collection. This extension is created in all databases in the cluster by default.