2018-01-01 19:04:05 +00:00
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permalink: "/{{ year }}/{{ month }}/{{ day }}/iterate-the-keyspace-in-redis-scan"
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2013-11-01 17:48:52 +00:00
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title: "Iterate the keyspace in redis: SCAN"
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2018-01-01 19:04:05 +00:00
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published_date: "2013-11-01 18:40:00 +0100"
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layout: post.liquid
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data:
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route: blog
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2013-11-01 17:48:52 +00:00
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---
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A few days ago antirez finally [merged][pr] the SCAN algorithm written by
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[Pieter Noordhuis](https://twitter.com/pnoordhuis). With it it's now possible
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to iterate the whole keyspace (or specific values in a set/sorted set/hash)
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without a huge performance impact on the rest of the server (as `KEYS` would do
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blocking on huge datasets).
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Read more about the usage in [antirez' blog][antirez-63] or read the implementation
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and explanation on [github][implementation] (I need to do that as well).
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For end users the usage is [documented][scan-docu].
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After the code was finally merged into unstable and 2.8 I sat down bringing
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that feature into the redis client library and with that also into
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[try.redis.io][tryredis]
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The client code is rather simple and was quickly merged ([461dd43][scan-in-rb])
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and is now also used in [try.redis][tryredis-scan].
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A small thing I discovered playing around and testing the new code was a
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crashing bug ([#1354][redis-crash]) with numeric values, but this was fixed as
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well. Another thing was that the 2.8 was not compiling after the fix was added,
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due to some new code only in the unstable branch. In absence of an official CI
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server for redis (we once had one, [but it's currently disabled][twitter-disabled]
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and will be back soon™) I went ahead and started the CI server on my own server:
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<http://tmp.fnordig.de/redis/ci/>
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Currently there is one failing test for 2.8 and unstable but I think we will get that fixed as well
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(just the memory efficiency test).
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With 2.8 already in RC-state we will soon have all the awesome new features in a stable redis release.
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[pr]: https://github.com/antirez/redis/pull/579
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[implementation]: https://github.com/antirez/redis/blob/dfeaa84d462a93070ee63ec87278a30d3105fa8d/src/dict.c#L663-L819
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[antirez-63]: http://antirez.com/news/63
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[scan-docu]: http://redis.io/commands/scan
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[scan-in-rb]: https://github.com/redis/redis-rb/commit/461dd435a7aa3f3b0077f481c5d4219913d6705c
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[redis-crash]: https://github.com/antirez/redis/issues/1354
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[tryredis-scan]: https://github.com/badboy/try.redis/commit/1601dd931607d2872b6387209290b43dc00ad7da
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[tryredis]: http://try.redis.io
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[twitter-disabled]: https://twitter.com/antirez/status/395964119859613697
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