Re: row filtering for logical replication

On Tue, Nov 16, 2021 at 7:33 PM tanghy.fnst@fujitsu.com
<tanghy.fnst@fujitsu.com> wrote:
>
> On Friday, November 12, 2021 6:20 PM Ajin Cherian <itsajin@gmail.com> wrote:
> >
> > Attaching version 39-
> >
>
> I met another problem when filtering out with the operator '~'.
> Data can't be replicated as expected.
>
> For example:
> -- publisher
> create table t (a text primary key);
> create publication pub for table t where (a ~ 'aaa');
>
> -- subscriber
> create table t (a text primary key);
> create subscription sub connection 'port=5432' publication pub;
>
> -- publisher
> insert into t values ('aaaaab');
> insert into t values ('aaaaabc');
> postgres=# select * from t where (a ~ 'aaa');
>     a
> ---------
>  aaaaab
>  aaaaabc
> (2 rows)
>
> -- subscriber
> postgres=# select * from t;
>    a
> --------
>  aaaaab
> (1 row)
>
> The second record can’t be replicated.
>
> By the way, when only applied 0001 patch, I couldn't reproduce this bug.
> So, I think it was related to the later patches.
>

I found that the problem was caused by allocating the WHERE clause
expression nodes in the wrong memory context (so they'd end up getting
freed after first-time use).

The following additions are needed in pgoutput_row_filter_init()  - patch 0005.

+ oldctx = MemoryContextSwitchTo(CacheMemoryContext);
  rfnode = stringToNode(TextDatumGetCString(rfdatum));
  rfnodes = lappend(rfnodes, rfnode);
+ MemoryContextSwitchTo(oldctx);

(these changes are needed in addition to the fixes I posted on this
thread for the crash problem that was previously reported)


Regards,
Greg Nancarrow
Fujitsu Australia