Horton

Re: WAL logging problem in 9.4.3?

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Martijn van Oosterhout <kleptog@svana.org>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2015-07-03T17:02:29Z
Lists: pgsql-hackers 
On 2015-07-03 18:49:31 +0200, Andres Freund wrote:
> But the more interesting question is why that's not hhappening
> today. RelationTruncateIndexes() does call the index_build() which
> should end up WAL logging the index creation.

So that's because there's an XLogIsNeeded() preventing it.

Maybe I'm just daft right now (35C outside, 32 inside, so ...), but I'm
right now missing how the whole "skip wal logging if relation has just
been truncated" optimization can ever actually be crashsafe unless we
use a new relfilenode (which we don't!).

Sure, we do an heap_sync() at the the end of the transaction. That's
nice and all. But it doesn't help if we crash and re-start WAL apply
from a checkpoint before the table was created. Because that'll replay
the truncation.

That's much worse than just the indexes - the rows added by a COPY
without WAL logging will also be truncated away, no?

Commits

  1. Add perl2host call missing from a new test file.

  2. Skip WAL for new relfilenodes, under wal_level=minimal.

  3. Revert "Skip WAL for new relfilenodes, under wal_level=minimal."

  4. Back-patch log_newpage_range().

  5. During heap rebuild, lock any TOAST index until end of transaction.

  6. In log_newpage_range(), heed forkNum and page_std arguments.

  7. Back-patch src/test/recovery and PostgresNode from 9.6 to 9.5.

  8. Reduce pg_ctl's reaction time when waiting for postmaster start/stop.

  9. Accelerate end-of-transaction dropping of relations

  10. Redesign the planner's handling of index-descent cost estimation.

  11. Make TRUNCATE do truncate-in-place when processing a relation that was created