9fb695d75c
Move cache TTL from `CachedSource` into the `CacheableSource` interface, allowing each source to define a TTL most appropriate to its own settings loading implementation. Fix bug where `generation` time was computed incorrectly by `CachedSource`. Include tests to exercise all `CachedSource` interactions with `CacheInterface` and `CacheableSource`. Bug: T296771 Change-Id: I97c42cf6ca716516c32104de25245aa21ec110e4
59 lines
2 KiB
PHP
59 lines
2 KiB
PHP
<?php
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namespace MediaWiki\Settings\Cache;
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use MediaWiki\Settings\Source\SettingsSource;
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/**
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* A {@link SettingsSource} that can be cached. It must return a unique
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* (enough) and deterministic hash key for cache indexing.
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*
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* @since 1.38
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* @todo mark as stable before the 1.38 release
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*/
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interface CacheableSource extends SettingsSource {
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/**
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* Returns the cache TTL (in seconds) for this source.
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*
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* @return int
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*/
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public function getExpiryTtl(): int;
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/**
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* Coefficient used in determining early expiration of cached settings to
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* avoid stampedes.
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*
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* Increasing this value will cause the random early election to happen by
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* a larger margin of lead time before normal expiry, relative to the
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* cache value's generation duration. Conversely, returning a lesser value
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* will narrow the margin of lead time, making the cache hold items for
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* slightly longer but with more likelihood that concurrent regenerations
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* and set overwrites will occur. Returning <code>0</code> will
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* effectively disable early expiration, and by extension disable stampede
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* mitigation altogether.
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*
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* A greater value may be suitable if a source has a highly variable
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* generation duration, but most implementations should simply return
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* <code>1.0</code>.
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*
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* @link https://en.wikipedia.org/wiki/Cache_stampede#Probabilistic_early_expiration
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* @link https://cseweb.ucsd.edu/~avattani/papers/cache_stampede.pdf
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*
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* Optimal Probabilistic Cache Stampede Prevention
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* Vattani, A.; Chierichetti, F.; Lowenstein, K. (2015), "Optimal
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* Probabilistic Cache Stampede Prevention" (PDF), Proceedings of the VLDB
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* Endowment, VLDB, 8 (8): 886–897, doi:10.14778/2757807.2757813, ISSN
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* 2150-8097 https://cseweb.ucsd.edu/~avattani/papers/cache_stampede.pdf
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*
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* @return float
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*/
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public function getExpiryWeight(): float;
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/**
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* Returns a deterministically computed key for use in caching settings
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* from this source.
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*
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* @return string
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*/
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public function getHashKey(): string;
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}
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