Note: starting with Redis 5, the replication method described in this section (scripts effects replication) is the default and does not need to be explicitly enabled.
Starting with Redis 3.2, it is possible to select an alternative replication method. Instead of replicating whole scripts, we can just replicate single write commands generated by the script. We call this script effects replication.
To enable script effects replication you need to issue the following Lua command before the script performs a write:
redis.replicate_commands()

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[Cache] invalidating tags breaks after updating to symfony/cache 5.3.3 with Redis versions below 5.x#42126

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nicolas-grekas commentedSep 24, 2021

<5 instead of <3? What about doDeleteYieldTags()?

wouterj changed the title~~[Cache] Fix invalidating tags on Redis <3~~[Cache] Fix invalidating tags on Redis <5

Sep 24, 2021

wouterj force-pushed theissue-42126/redis3-replication branch from7539aea to64784d2Compare

September 24, 2021 08:51

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This new replication method is only required when the commands are non deterministic. It seems like thedoDeleteYieldTags() script is deterministic. For completeness, I've started a redis:3 container locally and ran theRedisTagAwareAdapterTest integration tests with this container. They all passed with the changes in this PR.

I've also updated the PR to handle any exception better. Currently, users get a PHP Error: "Cannot use object of type RedisException as array". After this PR, they'll get the actual redis exception.

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September 24, 2021 08:54

wouterj changed the base branch from5.3 to4.4

September 24, 2021 08:55

wouterj modified the milestones:5.3,4.4

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September 24, 2021 09:01

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nicolas-grekas commentedSep 24, 2021

For my understanding, when did you encounterRedisException being returned? Is that a dev-time only issue or can this happen in regular operations? I'm asking because the cache adapters are not supposed to fail when there is an issue.

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wouterj commentedSep 24, 2021

We had this occur when invalidating caches in production.

I'm not sure what would be the best way forward. If there is an error, nothing is invalidated. So simply logging the exception and retuning would probably not be correct either.

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nicolas-grekas commentedSep 24, 2021•
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Do you know what theRedisException was about?

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Sep 25, 2021

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wouterj commentedSep 25, 2021•
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Do you know what the RedisException was about?

Yeah, it was about the error in the lua script that is fixed in this PR:

ERR Error running script (call to f_cea3ea3b59f1b3411febbbeb5f94de8a695cec73): @user_script:19: @user_script: 19: Write commands not allowed after non deterministic commands. Call redis.replicate_commands() at the start of your script in order to switch to single commands replication mode.

So in theory, you will not get this exception. But I don't know anything about Redis, so I guess maybe there is something else in this script that breaks for e.g. Redis 4 or Redis 6 in the future?

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nicolas-grekas commentedSep 25, 2021

Can we callCacheItem::log when we have the exception somehow?

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jderusse commentedSep 25, 2021

So in theory, you will not get this exception. But I don't know anything about Redis, so I guess maybe there is something else in this script that breaks for e.g. Redis 4 or Redis 6 in the future?

methodSSCAN is not deterministic (becauseSETs are unordered), that's why, in Redis 4, you have to tell Redis to replicate commands.

more infohttps://redis.io/commands/eval#replicating-commands-instead-of-scripts andhttps://redis.io/commands/EVAL#scripts-with-deterministic-writes

wouterj force-pushed theissue-42126/redis3-replication branch fromdbe0cf7 toeb09827Compare

September 25, 2021 11:08

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wouterj commentedSep 25, 2021

Can we callCacheItem::log when we have the exception somehow?

Oh, didn't know about this helper method. I've updated the PR with your suggestions: any exception is now logged and not thrown, anddoInvalidateTags() nows returnsfalse when there was an exception.