Re: row filtering for logical replication

Here are some review comments for v68-0001.

~~~

1. Commit message

"When a publication is defined or modified, rows that don't satisfy an
optional WHERE clause
will be filtered out."

That wording seems strange to me - it sounds like the filtering takes
place at the point of creating/altering.

Suggest reword something like:
"When a publication is defined or modified, an optional WHERE clause
can be specified. Rows that don't
satisfy this WHERE clause will be filtered out."

~~~

2. Commit message

"The WHERE clause allows simple expressions that don't have
user-defined functions, operators..."

Suggest adding the word ONLY:
"The WHERE clause only allows simple expressions that don't have
user-defined functions, operators..."

~~~

3. src/backend/replication/pgoutput/pgoutput.c - pgoutput_row_filter_init

+ /* If no filter found, clean up the memory and return */
+ if (!has_filter)
+ {
+ if (entry->cache_expr_cxt != NULL)
+ MemoryContextDelete(entry->cache_expr_cxt);
+
+ entry->exprstate_valid = true;
+ return;
+ }

IMO this should be refactored to have if/else, so the function has
just a single point of return and a single point where the
exprstate_valid is set. e.g.

if (!has_filter)
{
/* If no filter found, clean up the memory and return */
...
}
else
{
/* Create or reset the memory context for row filters */
...
/*
* Now all the filters for all pubactions are known. Combine them when
* their pubactions are same.
...
}

entry->exprstate_valid = true;

~~~

4. src/backend/replication/pgoutput/pgoutput.c - pgoutput_row_filter comment

+ /*
+ * We need this map to avoid relying on changes in ReorderBufferChangeType
+ * enum.
+ */
+ static int map_changetype_pubaction[] = {
+ [REORDER_BUFFER_CHANGE_INSERT] = PUBACTION_INSERT,
+ [REORDER_BUFFER_CHANGE_UPDATE] = PUBACTION_UPDATE,
+ [REORDER_BUFFER_CHANGE_DELETE] = PUBACTION_DELETE
+ };

Suggest rewording comment and remove the double-spacing:

BEFORE:
"We need this map to avoid relying on changes in ReorderBufferChangeType enum."

AFTER:
"We need this map to avoid relying on ReorderBufferChangeType enums
having specific values."

~~~

5. DEBUG level 3

I found there are 3 debug logs in this patch and they all have DEBUG3 level.

IMO it is probably OK as-is, but just a comparison I noticed that the
most detailed logging for logical replication worker.c was DEBUG2.
Perhaps row-filter patch should be using DEBUG2 also?

------
Kind Regards,
Peter Smith.
Fujitsu Australia