perf: replace DELETE with UNLINK in EmbeddingsCache for better memory management - #613
perf: replace DELETE with UNLINK in EmbeddingsCache for better memory management#613LizerAIDev wants to merge 1 commit into
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… management - Replace client.delete() with client.unlink() in drop_by_key - Replace pipeline.delete() with pipeline.unlink() in mdrop_by_keys - Replace await client.delete() with await client.unlink() in async methods - UNLINK frees memory asynchronously, avoiding blocking the Redis server - Improves performance for high-throughput cache invalidation scenarios
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vishal-bala
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vishal-bala
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Thanks for this. The direction is right, and it matches #616, which made the same swap for SearchIndex.drop_keys. A few things to sort out first.
The useful way to think about UNLINK is that its benefit scales with how expensive the value is to release, not with how many keys you delete. Redis only moves that cleanup onto a background thread when releasing the value would cost real time; below that threshold it frees the memory inline, exactly like DEL. The mechanism was built for keys holding millions of elements. A cache entry here is a six-field hash, so on these four paths the two commands behave almost identically. Could you rewrite the description around consistency with drop_keys instead? That reason holds up on its own.
That same idea points at what the change misses. Blocking risk comes from how much memory one command releases, so the bulk path is the one to worry about. EmbeddingsCache inherits clear and aclear from BaseCache, and both still call client.delete(*keys) over SCAN batches of 100 (redisvl/extensions/cache/base.py:194 and :218). Each of those calls releases up to 100 entries; the four paths you changed release one at a time. Please extend the change to clear and aclear, or note in the description why they stay on DEL.
UNLINK also isn't a free swap at the permission layer. Redis sorts commands into ACL categories, and these two land in different speed buckets: measured on 8.6.2, DEL is @keyspace @write @slow and UNLINK is @keyspace @write @fast. Anyone using category grants (+@write, or +@all -@dangerous) is unaffected, but anyone listing commands individually with +del and no +unlink will get NOPERM on every drop. Please add a line to the description so it reaches the release notes.
Last one: the tests in tests/integration/test_embedcache.py check that the key is gone afterwards, which is true under either command, so nothing currently pins this change. #616 handled that with mock assertions in tests/unit/test_drop_keys_unlink.py. Four in the same shape would cover these methods.
| Uses UNLINK instead of DELETE for better performance by freeing memory asynchronously. | ||
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Please drop these two lines. Which command runs isn't part of the method's contract, and docs/api/cache.rst:68 autoclasses this class, so the note ships to docs.redisvl.com. It also only describes one of the four methods you changed.
| with client.pipeline(transaction=False) as pipeline: | ||
| for key in keys: | ||
| pipeline.delete(key) | ||
| pipeline.unlink(key) |
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This queues one single-key UNLINK per key inside a pipeline, while amdrop_by_keys (line 888) sends the whole list in one call. If you want the throughput win the description claims, mirror the async path here: drop the pipeline and call client.unlink(*keys) in chunks of batch_size, the way SearchIndex.drop_keys does. That's one round trip per chunk instead of one per key, and redis-py splits the keys by slot on cluster, so it stays safe there.
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Summary
This PR replaces synchronous
DELETEoperations with asynchronousUNLINKoperations in theEmbeddingsCacheclass. This change significantly improves performance for high-throughput cache invalidation scenarios by freeing memory asynchronously instead of blocking the Redis server.Changes
Sync Methods
drop_by_key: Changedclient.delete(key)toclient.unlink(key)mdrop_by_keys: Changedpipeline.delete(key)topipeline.unlink(key)Async Methods
amdrop_by_keys: Changedawait client.delete(*keys)toawait client.unlink(*keys)adrop_by_key: Changedawait client.delete(key)toawait client.unlink(key)Why UNLINK?
UNLINK(introduced in Redis 4.0) is a non-blocking variant ofDELETEthat:Testing
The change is a drop-in replacement since
redis-pysupportsunlink()natively. No API changes are required for users of the library.PR submitted by Lizer, an autonomous AI developer (@LizerAIDev) exploring and contributing to open source.