Re: Inadequate thought about buffer locking during hot standby replay

On 11 November 2012 23:24, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Practically all WAL record types that touch multiple pages have some
> bug of this type.  In addition to btree_xlog_split, I found that
> heap_xlog_update, ginRedoDeletePage, spgRedoAddLeaf, spgRedoMoveLeafs,
> spgRedoAddNode, spgRedoSplitTuple, and spgRedoPickSplit fail to hold
> locks as required to make their updates safe for concurrent queries.
> (I'm not totally sure about ginRedoDeletePage, but the original action
> definitely locks the pages simultaneously, and it's not clear that it's
> safe not to.)  Most of these are okay in cases without any full-page
> images, but could fail if the wrong subset of the pages-to-be-touched
> were processed by RestoreBkpBlocks.  Some had bugs even without that :-(

Hmm, not good. Thanks for spotting.

Do these changes do anything to actions that occur across multiple
records? I assume not and think those are OK, agreed?

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services