Re: [PATCH] Logical decoding of TRUNCATE

This sounds like a good approach.

> +static void
> +pg_decode_truncate(LogicalDecodingContext *ctx, ReorderBufferTXN *txn,
> + int nrelations, Relation relations[], ReorderBufferChange *change)
> +{

> + for (i = 0; i < nrelations; i++)
> + {
> + Oid relid = RelationGetRelid(relations[i]);
> +
> + if (i > 0)
> + appendStringInfoString(ctx->out, ", ");
> +
> + appendStringInfoString(ctx->out,
> + quote_qualified_identifier(
> + get_namespace_name(get_rel_namespace(relid)),
> + get_rel_name(relid)));

Note that you start the loop having the Relation; yet you go extra
length to grab the relnamespace and relname from syscache instead of
just relations[i]->rd_rel->relname etc.

pgoutput doesn't do it that way, so it doesn't affect logical
replication, but I think it's best not to create awkward code in
test_decoding, since it's so widely copied.

> + else if (info == XLOG_HEAP_TRUNCATE)
> + {
> + xl_heap_truncate *xlrec = (xl_heap_truncate *) rec;
> +
> + if (xlrec->flags & XLH_TRUNCATE_CASCADE)
> + appendStringInfo(buf, "cascade ");
> + if (xlrec->flags & XLH_TRUNCATE_RESTART_SEQS)
> + appendStringInfo(buf, "restart_seqs ");
> + appendStringInfo(buf, "nrelids %u", xlrec->nrelids);
> + /* skip the list of relids */
> + }

Maybe not a big deal, but for future pg_waldump users I'm sure it'll be
nice to have the OIDs here.

> +void
> +ExecuteTruncateGuts(List *explicit_rels, List *relids, List *relids_logged,
> + DropBehavior behavior, bool restart_seqs)
> +{

Please add a comment atop this function.

> + /*
> + * Write a WAL record to allow this set of actions to be logically decoded.
> + *
> + * Assemble an array of relids so we can write a single WAL record for the
> + * whole action.
> + */
> + if (list_length(relids_logged) > 0)
> + {
> + xl_heap_truncate xlrec;
> + int i = 0;

I wonder if this should happen only if logical decoding? (Maybe it
already occurs because relids_logged would be empty? Worth a comment in
that case)

--
Álvaro Herrera https://www.2ndQuadrant.com/
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