Re: Support logical replication of DDLs - Mailing list pgsql-hackers

On Thu, Apr 20, 2023 at 2:28 PM shveta malik <shveta.malik@gmail.com> wrote:
>
> On Thu, Apr 20, 2023 at 9:11 AM shveta malik <shveta.malik@gmail.com> wrote:
>>
>> On Mon, Apr 17, 2023 at 5:32 PM Zhijie Hou (Fujitsu)
>> <houzj.fnst@fujitsu.com> wrote:
>> >
>> > Attach the new version patch set which include the following changes:
>> Few comments for ddl_deparse.c in patch dated April17:
>>
>  Few comments for ddl_json.c in the patch dated April17:
>

Few more comments, mainly for event_trigger.c  in the patch dated April17:

1)EventTriggerCommonSetup()
+    pub_funcoid = LookupFuncName(pubfuncname, 0, NULL, true);

This is the code where we have special handling for ddl-triggers. Here
we are passing 'missing_ok' as true, so shouldn't we check pub_funcoid
against 'InvalidOid' ?


2) EventTriggerTableInitWriteEnd()

+ if (stmt->objtype == OBJECT_TABLE)
+ {
+    parent = currentEventTriggerState->currentCommand->parent;
+    pfree(currentEventTriggerState->currentCommand);
+    currentEventTriggerState->currentCommand = parent;
+ }
+ else
+ {
+    MemoryContext oldcxt;
+    oldcxt = MemoryContextSwitchTo(currentEventTriggerState->cxt);
+    currentEventTriggerState->currentCommand->d.simple.address = address;
+    currentEventTriggerState->commandList =
+         lappend(currentEventTriggerState->commandList,
+     currentEventTriggerState->currentCommand);
+
+     MemoryContextSwitchTo(oldcxt);
+ }
+}

It will be good to add some comments in the 'else' part. It is not
very much clear what exactly we are doing here and for which scenario.


3) EventTriggerTableInitWrite()

+ if (!currentEventTriggerState)
+     return;
+
+ /* Do nothing if no command was collected. */
+ if (!currentEventTriggerState->currentCommand)
+      return;

Is it possible that when we reach here no command is collected yet? I
think this can happen only for the case when
commandCollectionInhibited is true. If so, above can be modified to:

        if (!currentEventTriggerState ||
                currentEventTriggerState->commandCollectionInhibited)
                return;
        Assert(currentEventTriggerState->currentCommand != NULL);

This will make the behaviour and checks consistent across similar
functions in this file.


4) EventTriggerTableInitWriteEnd()
Here as well, we can have the same assert as below:
 Assert(currentEventTriggerState->currentCommand != NULL);
'currentEventTriggerState' and 'commandCollectionInhibited' checks are
already present.

5) logical_replication.sgml:
 +  'This is especially useful if you have lots schema changes over
time that need replication.'

 lots schema --> lots of schema

thanks
Shveta