Re: Torn page hazard in ginRedoUpdateMetapage()

On 03/10/2014 09:44 PM, Robert Haas wrote:
> On Mon, Apr 30, 2012 at 1:34 PM, Noah Misch <noah(at)leadboat(dot)com> wrote:
>> When GIN changes a metapage, we WAL-log its ex-header content and never use a
>> backup block. This reduces WAL volume since the vast majority of the metapage
>> is unused. However, ginRedoUpdateMetapage() only restores the WAL-logged
>> content if the metapage LSN predates the WAL record LSN. If a metapage write
>> tore and updated the LSN but not the other content, we would fail to complete
>> the update. Instead, unconditionally reinitialize the metapage similar to how
>> _bt_restore_meta() handles the situation.
>>
>> I found this problem by code reading and did not attempt to build a test case
>> illustrating its practical consequences. It's possible that there's no
>> problem in practice on account of some reason I haven't contemplated.
>
> The attached patch doesn't apply any more, but it looks like this
> issue still exists.

Fixed.

- Heikki