Re: Write Ahead Logging for Hash Indexes

On Thu, Mar 9, 2017 at 11:15 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Thu, Mar 9, 2017 at 10:23 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> Right, if we use XLogReadBufferForRedoExtended() instead of
>> XLogReadBufferExtended()/LockBufferForCleanup during relay routine,
>> then it will restore FPI when required and can serve our purpose of
>> acquiring clean up lock on primary bucket page. Yet another way could
>> be to store some information like block number, relfilenode, forknum
>> (maybe we can get away with some less info) of primary bucket in the
>> fixed part of each of these records and then using that read the page
>> and then take a cleanup lock. Now, as in most cases, this buffer
>> needs to be registered only in cases when there are multiple overflow
>> pages, I think having fixed information might hurt in some cases.
>
> Just because the WAL record gets larger? I think you could arrange to
> record the data only in the cases where it is needed, but I'm also not
> sure it would matter that much anyway. Off-hand, it seems better than
> having to mark the primary bucket page dirty (because you have to set
> the LSN) every time any page in the chain is modified.
>

Do we really need to set LSN on this page (or mark it dirty), if so
why? Are you worried about restoration of FPI or something else?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com