Add command being unblocked cause another command to get unblocked execution order test #12324
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…ecution order test In redis#12301, we observed that if the `while(listLength(server.ready_keys) != 0)` in handleClientsBlockedOnKeys is changed to `if(listLength(server.ready_keys) != 0)`, the order of command execution will change. It is wrong to change that. It means that if a command being unblocked causes another command to get unblocked (like a BLMOVE would do), then the new unblocked command will wait for later to get processed rather than right away. It'll not have any real implication if we change that since we do call handleClientsBlockedOnKeys in beforeSleep again, and redis will still behave correctly, but we don't change that. An example: 1. $rd1 blmove src{t} dst{t} left right 0 2. $rd2 blmove dst{t} src{t} right left 0 3. $rd3 set key1{t}, $rd3 lpush src{t}, $rd3 set key2{t} in a pipeline The correct order would be: 1. set key1{t} 2. lpush src{t} 3. lmove src{t} dst{t} left right 4. lmove dst{t} src{t} right left 5. set key2{t} The wrong order would be: 1. set key1{t} 2. lpush src{t} 3. lmove src{t} dst{t} left right 4. set key2{t} 5. lmove dst{t} src{t} right left This PR adds corresponding test to cover it.
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oranagra
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i now realize that we can also easily write a test that will really get the wrong command result (not just based on order of things in the replication stream).
i.e. if the command after the pipeline would access the src key, it'll get a different result depending on whether the second BLMOVE runs first or not.
but anyway, that test is certainly sufficient to detect the bug next time it happens.
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In #12301, we observed that if the
while(listLength(server.ready_keys) != 0)in handleClientsBlockedOnKeys is changed to
if(listLength(server.ready_keys) != 0),the order of command execution will change.
It is wrong to change that. It means that if a command
being unblocked causes another command to get unblocked
(like a BLMOVE would do), then the new unblocked command
will wait for later to get processed rather than right away.
It'll not have any real implication if we change that since
we do call handleClientsBlockedOnKeys in beforeSleep again,
and redis will still behave correctly, but we don't change that.
An example:
The correct order would be:
The wrong order would be:
This PR adds corresponding test to cover it.