Re: WAL consistency check facility

Hello Simon,

I'm really sorry for the inconveniences. Next time, I'll attach the
patch with proper documentation, test and comments.

> I think you should add this as part of the default testing for both
> check and installcheck. I can't imagine why we'd have it and not use
> it during testing.

Since, this is redo(replay) feature, we can surely add this in
installcheck. But, as Amit mentioned, it could be time-consuming.

>> * 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)

>> 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.

--
Thanks & Regards,
Kuntal Ghosh
EnterpriseDB: http://www.enterprisedb.com