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Detail the issue of redirection occurring within a transaction. #168

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Detail the issue of redirection occurring within a transaction. #168

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29 changes: 28 additions & 1 deletion topics/transactions.md
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Original file line number Diff line number Diff line change
Expand Up @@ -120,10 +120,37 @@ MULTI
+OK
INCR a b c
-ERR wrong number of arguments for 'incr' command
EXEC
-EXECABORT Transaction discarded because of previous errors.
```

This time due to the syntax error the bad `INCR` command is not queued
at all.
at all. And the `EXEC` command will receive an `EXECABORT` error.

There are some more specific scenarios: in the `MULTI` context, commands are
successfully queued (i.e., `QUEUED` reply is received), but when the `EXEC` command
is executed, it is found that the data needed for these commands does not belong to
the current node (for example, in cluster mode, the accessed slot has been migrated to
another node; in standalone mode, a primary-replica switch has occurred). In this case,
the `EXEC` command will receive a `MOVED` or `REDIRECT` result.
Comment on lines +130 to +135
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Suggested change
There are some more specific scenarios: in the `MULTI` context, commands are
successfully queued (i.e., `QUEUED` reply is received), but when the `EXEC` command
is executed, it is found that the data needed for these commands does not belong to
the current node (for example, in cluster mode, the accessed slot has been migrated to
another node; in standalone mode, a primary-replica switch has occurred). In this case,
the `EXEC` command will receive a `MOVED` or `REDIRECT` result.
When the `EXEC` command is processed, the server will check if a failover or slot migration has occurred since queuing the commands.
If either event has occurred, a `-MOVED` or `-REDIRECT` error will be returned if needed without processing the transaction.

I think just being a bit more succinct for what the user will see might make the English problem easier?

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can we also clarify when -MOVED/-REDIRECR would be expected as well? I feel like the table (option 1) at valkey-io/valkey#895 (comment) is very helpful. It would be great if it could be incorporated in this doc.


For cluster mode:

```
MULTI ==> +OK
SET x y ==> +QUEUED
slot {x} is migrated to other node
EXEC ==> -MOVED
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I didn't see the EXECABORT behavior documented in this file or anywhere in the doc repo. Can we add it here too for completeness?

```

For standalone mode:

```
MULTI ==> +OK
SET x y ==> +QUEUED
failover
EXEC ==> -REDIRECT
```

## What about rollbacks?

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