forked from TrueCloudLab/frostfs-node
[#1745] writecache: Actualize docs
Signed-off-by: Evgenii Stratonikov <evgeniy@morphbits.ru>support/v0.34
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@ -1,20 +1,11 @@
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// Package writecache implements write-cache for objects.
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//
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// It contains in-memory cache of fixed size and underlying database
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// (usually on SSD) for storing small objects.
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// There are 3 places where object can be:
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// 1. In-memory cache.
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// 2. On-disk cache DB.
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// 3. Main storage (blobstor).
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// Write-cache has 2 components:
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// 1. Key-value (bbolt) database for storing small objects.
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// 2. Filesystem tree for storing big objects.
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//
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// There are 2 types of background jobs:
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// 1. Persisting objects from in-memory cache to database.
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// 2. Flushing objects from database to blobstor.
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// On flushing object address is put in in-memory LRU cache.
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// The actual deletion from the DB is done when object
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// is evicted from this cache.
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//
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// Putting objects to the main storage is done by multiple workers.
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// Some of them prioritize flushing items, others prioritize putting new objects.
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// The current ration is 50/50. This helps to make some progress even under load.
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// Flushing from the writecache to the main storage is done in the background.
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// To make it possible to serve Read requests after the object was flushed,
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// we maintain an LRU cache containing addresses of all the objects that
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// could be safely deleted. The actual deletion is done during eviction from this cache.
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package writecache
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@ -185,9 +185,7 @@ func (c *cache) flushBigObjects() {
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}
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}
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// flushWorker runs in a separate goroutine and write objects to the main storage.
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// If flushFirst is true, flushing objects from cache database takes priority over
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// putting new objects.
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// flushWorker writes objects to the main storage.
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func (c *cache) flushWorker(_ int) {
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defer c.wg.Done()
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