Re: WAL consistency check facility

On Wed, Aug 31, 2016 at 10:32 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> On 27 August 2016 at 12:09, Kuntal Ghosh <kuntalghosh.2007@gmail.com> wrote:
>
>>>> * wal_consistency_mask = 511  /* Enable consistency check mask bit*/
>>>
>>> What does this mean? (No docs)
>>
>> I was using this parameter as a masking integer to indicate the
>> operations(rmgr list) for which we need this feature to be enabled.
>> Since, this could be confusing, I've changed it accordingly so that it
>> accepts a list of rmgrIDs. (suggested by Michael, Amit and Robert)
>
> Why would we want that?

I am still in for just an on/off switch instead of this complication.
An all-or-nothing feature is what we are looking at here. Still a list
is an improvement compared to a bitmap.

>>>> 1. Add support for other Resource Managers.
>>>
>>> We probably need to have a discussion as to why you think this should
>>> be Rmgr dependent?
>>> Code comments would help there.
>>>
>>> If it does, then you should probably do this by extending RmgrTable
>>> with an rm_check, so you can call it like this...
>>>
>>> RmgrTable[record->xl_rmid].rm_check
>>
>> +1.
>> I'm modifying it accordingly. I'm calling this function after
>> RmgrTable[record->xl_rmid].rm_redo.
>>
>>>> 5. Generalize the page type identification technique.
>>>
>>> Why not do this first?
>>>
>>
>> At present, I'm using special page size and page ID to identify page
>> type. But, I've noticed some cases where the entire page is
>> initialized to zero (Ex: hash_xlog_squeeze_page). RmgrID and info bit
>> can help us to identify those pages.
>
> I'd prefer a solution that was not dependent upon RmgrID at all.

So you'd rather identify the page types by looking at pd_special? That
seems worse to me but..
-- 
Michael