Re: Setting pd_lower in GIN metapage

On Wed, Jun 21, 2017 at 9:42 AM, Amit Langote
<Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> On 2017/06/20 20:37, Amit Kapila wrote:
>> On Tue, Jun 20, 2017 at 1:50 PM, Amit Langote
>> <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>> On 2017/06/19 23:31, Tom Lane wrote:
>>>> I'd suggest a rule like "if pd_lower is smaller than SizeOfPageHeaderData
>>>> then don't trust it, but assume all of the page is valid data".
>>>
>>> Actually, such a check is already in place in the tool, whose condition
>>> looks like:
>>>
>>> if (PageGetPageSize(header) == BLCKSZ &&
>>> PageGetPageLayoutVersion(header) == PG_PAGE_LAYOUT_VERSION &&
>>> (header->pd_flags & ~PD_VALID_FLAG_BITS) == 0 &&
>>> header->pd_lower >= SizeOfPageHeaderData &&
>>> header->pd_lower <= header->pd_upper &&
>>> header->pd_upper <= header->pd_special &&
>>> header->pd_special <= BLCKSZ &&
>>> header->pd_special == MAXALIGN(header->pd_special) && ...
>>>
>>> which even GIN metapage passes, making it an eligible data page and hence
>>> for omitting the hole between pd_lower and pd_upper.
>>>
>>
>> Won't checking for GIN_META in header->pd_flags gives you what you want?
>
> GIN_META flag is not written into pd_flags but GinPageOpaqueData.flags,
> which still requires including GIN's private header.

Did you check this patch with wal_consistency_checking? I am getting
failures so your patch does not have the masking of GIN pages
completely right:
FATAL: inconsistent page found, rel 1663/16385/28133, forknum 0, blkno 0
CONTEXT: WAL redo at 0/39379EB8 for Gin/UPDATE_META_PAGE:
That's easily reproducible with installcheck and a standby replaying
the changes. I did not look at the code in details to see what you may
be missing here.
--
Michael