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Update pgxn/neon/relperst_cache.c

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Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
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Konstantin Knizhnik
2025-07-23 15:58:33 +03:00
committed by Konstantin Knizhnik
parent 6164f5eaeb
commit dd1440960a
1 changed files with 9 additions and 10 deletions
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19
pgxn/neon/relperst_cache.c
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@@ -29,18 +29,17 @@
#endif
/*
* The main goal of this cache is to avoid calls of mdexists in neon_write,
* The main goal of this cache is to avoid repeated calls of mdexists in neon_write,
* which is needed to distinguish unlogged relations.
* It has a fixed size, implementing eviction with the LRU algorithm.
*
* This hash is also used to mark relation during unlogged build.
* It has limited size, implementing eviction based on LRU algorithm.
* Relations involved in unlogged build are pinned in the cache (assuming that
* number of concurrent unlogged build is small.
*
* Another task of this hash is to prevent race condition during unlogged build termination.
* Some backend may want to evict page which backenf performing unlogged build can complete it and unlinking local files.
* We are using shared lock which is hold during all write operation. As far as lock is shared is doesn't prevent concurrent writes.
* Exclusive lock is taken by unlogged_build_end to change relation kind.
* This hash is also used to mark a relation during an unlogged build.
* Relations involved in unlogged build are pinned in the cache and never evicted. (Relying
* on the fact that the number of concurrent unlogged builds is small). Evicting a page
* belonging to an unlogged build involves an extra locking step to eliminate a race condition
* between unlogged build completing and deleted the local file, at the same time that
* another backend is evicting a page belonging to it. See how `finish_unlogged_build_lock`
* is used in `neon_write`
*/
typedef struct