Re: Skip collecting decoded changes of already-aborted transactions - Mailing list pgsql-hackers

Hi Sawada-San, here are some review comments for the patch v5-0001.

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Commit message.

1.
This commit introduces an additional check to determine if a
transaction is already aborted by a CLOG lookup, so the logical
decoding skips further change also when it doesn't touch system
catalogs.

~

Is that wording backwards? Is it meant to say:

This commit introduces an additional CLOG lookup check to determine if
a transaction is already aborted, so the ...

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contrib/test_decoding/sql/stats.sql

2
+SELECT slot_name, spill_txns = 0 AS spill_txn, spill_count = 0 AS
spill_count FROM pg_stat_replication_slots WHERE slot_name =
'regression_slot_stats4_twophase';

Why do the SELECT "= 0" like this, instead of just having zeros in the
"expected" results?

======
.../replication/logical/reorderbuffer.c

3.
 static void ReorderBufferTruncateTXN(ReorderBuffer *rb, ReorderBufferTXN *txn,
- bool txn_prepared);
+ bool txn_prepared, bool mark_streamed);

That last parameter name ('mark_streamed') does not match the same
parameter name in this function's definition.

~~~

ReorderBufferTruncateTXN:

4.
if (txn_streaming && (!txn_prepared) &&
  (rbtxn_is_toptxn(txn) || (txn->nentries_mem != 0)))
  txn->txn_flags |= RBTXN_IS_STREAMED;

if (txn_prepared)
{
~

Since the following condition was already "if (txn_prepared)" would it
be better remove the "(!txn_prepared)" here and instead just refactor
the code like:

if (txn_prepared)
{
  ...
}
else if (txn_streaming && (rbtxn_is_toptxn(txn) || (txn->nentries_mem != 0)))
{
  ...
}

~~~

ReorderBufferProcessTXN:

5.
+
+ /* Remember the transaction is aborted */
+ Assert((curtxn->txn_flags & RBTXN_IS_COMMITTED) == 0);
+ curtxn->txn_flags |= RBTXN_IS_ABORTED;

Missing period on comment.

~~~

ReorderBufferCheckTXNAbort:

6.
+ * If GUC 'debug_logical_replication_streaming' is "immediate", we don't
+ * check the transaction status, so the caller always processes this
+ * transaction. This is to disable this check for regression tests.
+ */
+static bool
+ReorderBufferCheckTXNAbort(ReorderBuffer *rb, ReorderBufferTXN *txn)
+{
+ /*
+ * If GUC 'debug_logical_replication_streaming' is "immediate", we don't
+ * check the transaction status, so the caller always processes this
+ * transaction.
+ */
+ if (unlikely(debug_logical_replication_streaming ==
DEBUG_LOGICAL_REP_STREAMING_IMMEDIATE))
+ return false;
+

The wording of the sentence "This is to disable..." seemed a bit
confusing. Maybe this area can be simplified by doing the following.

6a.
Change the function comment to say more like below:

When the GUC 'debug_logical_replication_streaming' is set to
"immediate", we don't check the transaction status, meaning the caller
will always process this transaction. This mode is used by regression
tests to avoid unnecessary transaction status checking.

~

6b.
It is not necessary for this 2nd comment to repeat everything that was
already said in the function comment. A simpler comment here might be
all you need:

SUGGESTION:
Quick return for regression tests.

~~~

7.
Is it worth mentioning about this skipping of the transaction status
check in the docs for this GUC? [1]

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[1] https://www.postgresql.org/docs/devel/runtime-config-developer.html

Kind Regards,
Peter Smith.
Fujitsu Australia.