fix: Support replicating Valkey and Redis 7.2 #3927
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Until now, we only tested Dragonfly against Redis 6.2. It appears that something has changed in the way Redis sends stable sync commands, and now they also forward `MULTI` and `EXEC` as part of their replication. Since we do not allow all commands to run under `MULTI`/`EXEC`, specifically `SELECT`, a Dragonfly replica of such servers failed these commands and became inconsistent with the data on the master. The proposed fix is to simply ignore (i.e. not execute) `MULTI`/`EXEC` coming from a Redis/Valkey master, and run the commands within those transactions individually, like we do for other transactions. To test this we randomly choose a redis/valkey server based on 3 available installed binaries and test against them.
chakaz
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Oct 15, 2024
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| // Valkey and Redis may send MULTI and EXEC as part of their replication commands. | ||
| // Dragonfly disallows some commands, such as SELECT, inside of MULTI/EXEC, so here we simply | ||
| // ignore MULTI/EXEC and execute their inner commands individually. | ||
| if (!absl::EqualsIgnoreCase(cmd, "MULTI") && !absl::EqualsIgnoreCase(cmd, "EXEC")) { |
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The only change here is the added if (with comments), and the usage of cmd in the VLOG below
adiholden
approved these changes
Oct 15, 2024
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Until now, we only tested Dragonfly against Redis 6.2. It appears that something has changed in the way Redis sends stable sync commands, and now they also forward
MULTIandEXECas part of their replication.Since we do not allow all commands to run under
MULTI/EXEC, specificallySELECT, a Dragonfly replica of such servers failed these commands and became inconsistent with the data on the master.The proposed fix is to simply ignore (i.e. not execute)
MULTI/EXECcoming from a Redis/Valkey master, and run the commands within those transactions individually, like we do for other transactions.To test this we randomly choose a redis/valkey server based on 3 available installed binaries and test against them.