In #11012, we changed the way command durations were computed to handle
the same command being executed multiple times. In #11970, we added an
assert if the duration is not properly reset, potentially indicating
that a call to report statistics was missed.
I found an edge case where this happens - easily reproduced by blocking
a client on `XGROUPREAD` and migrating the stream's slot. This causes
the engine to process the `XGROUPREAD` command twice:
1. First time, we are blocked on the stream, so we wait for unblock to
come back to it a second time. In most cases, when we come back to
process the command second time after unblock, we process the command
normally, which includes recording the duration and then resetting it.
2. After unblocking we come back to process the command, and this is
where we hit the edge case - at this point, we had already migrated the
slot to another node, so we return a `MOVED` response. But when we do
that, we don’t reset the duration field.
Fix: also reset the duration when returning a `MOVED` response. I think
this is right, because the client should redirect the command to the
right node, which in turn will calculate the execution duration.
Also wrote a test which reproduces this, it fails without the fix and
passes with it.
---------
Signed-off-by: Nitai Caro <caronita@amazon.com>
Co-authored-by: Nitai Caro <caronita@amazon.com>
This aligns the behaviour with established Valkey commands with a
TIMEOUT argument, such as BLPOP.
Fix#422
Signed-off-by: Ping Xie <pingxie@google.com>
After READONLY, make a cluster replica behave as its primary regarding
returning ASK redirects and TRYAGAIN.
Without this patch, a client reading from a replica cannot tell if a key
doesn't exist or if it has already been migrated to another shard as
part of an ongoing slot migration. Therefore, without an ASK redirect in
this situation, offloading reads to cluster replicas wasn't reliable.
Note: The target of a redirect is always a primary. If a client wants to
continue reading from a replica after following a redirect, it needs to
figure out the replicas of that new primary using CLUSTER SHARDS or
similar.
This is related to #21 and has been made possible by the introduction of
Replication of Slot Migration States in #445.
----
Release notes:
During cluster slot migration, replicas are able to return -ASK
redirects and -TRYAGAIN.
---------
Signed-off-by: Viktor Söderqvist <viktor.soderqvist@est.tech>
