Hi,
On Thu, Dec 18, 2025 at 06:22:40PM +0530, Ashutosh Bapat wrote:
> Hi Bertrand,
>
> On Wed, Dec 17, 2025 at 2:12 PM Bertrand Drouvot
> <[email protected]> wrote:
> >
> > What worries me is all those API changes:
> >
> > -typedef void (*LogicalDecodeChangeCB) (struct LogicalDecodingContext *ctx,
> > +typedef bool (*LogicalDecodeChangeCB) (struct LogicalDecodingContext *ctx,
> >
> > Those changes will break existing third party logical decoding plugin, even
> > ones
> > that don't want the new statistics features.
> >
> > What about not changing those and just add a single new optional callback,
> > say?
> >
> > typedef void (*LogicalDecodeReportStatsCB)(
> > LogicalDecodingContext *ctx,
> > ReorderBufferTXN *txn,
> > bool *transaction_sent,
> > size_t *bytes_filtered
> > );
> >
> > This way:
> >
> > - Existing plugins can still work without modification
> > - New or existing plugins can choose to provide statistics
> >
>
> I think that it will bring back the same problems that the previous
> design had or am I missing something?
I think that my example was confusing due to "size_t *bytes_filtered". I think
that what we could do is something like:
"
typedef void (*LogicalDecodeReportStatsCB)(
LogicalDecodingContext *ctx,
LogicalDecodeEventType event_type,
bool *filtered,
bool *txn_sent);
"
Note that there is no more size_t.
Then for, for example in change_cb_wrapper(), we could do:
"
ctx->callbacks.change_cb(ctx, txn, relation, change);
if (ctx->callbacks.report_stats_cb)
{
bool filtered = false;
ctx->callbacks.report_stats_cb(ctx, LOGICALDECODE_CHANGE,
&filtered,
NULL);
if (filtered)
cache->filteredBytes += ReorderBufferChangeSize(change);
}
"
The plugin would need to "remember" that it filtered (so that it can
reply to the callback). It could do that by adding say "last_event_filtered" to
it's output_plugin_private structure.
That's more work on the plugin side and we would probably need to provide some
examples from our side.
I think the pros are that:
- plugins that don't want to report stats would have nothing to do (no breaking
changes)
- the core does the computation
Thoughts?
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
