On Tue, Sep 19, 2017 at 9:27 AM, Michael Paquier <michael.paqu...@gmail.com> wrote: > On Tue, Sep 19, 2017 at 12:40 PM, Amit Kapila <amit.kapil...@gmail.com> wrote: >> On Mon, Sep 18, 2017 at 4:03 PM, Michael Paquier >> <michael.paqu...@gmail.com> wrote: >>> On Mon, Sep 18, 2017 at 11:16 AM, Amit Kapila <amit.kapil...@gmail.com> >>> wrote: >>>> On Sat, Sep 16, 2017 at 7:15 PM, Michael Paquier >>>> <michael.paqu...@gmail.com> wrote: >>>>> >>>> >>>> You have already noticed above that it will help when >>>> wal_checking_consistency is used and that was the main motivation to >>>> pass REGBUF_STANDARD apart from maintaining consistency. It is not >>>> clear to me what is bothering you. If your only worry about these >>>> patches is that you want this sentence to be removed from the comment >>>> because you think it is obvious or doesn't make much sense, then I >>>> think we can leave this decision to committer. I have added it based >>>> on Tom's suggestion above thread about explaining why it is >>>> inessential or essential to set pd_lower. I think Amit Langote just >>>> tried to mimic what I have done in hash and btree patches to maintain >>>> consistency. I am also not very sure if we should write some detailed >>>> comment or leave the existing comment as it is. I think it is just a >>>> matter of different perspective. >>> >>> What is disturbing me a bit is that the existing comments mention >>> something that could be supported (the compression of pages), but >>> that's actually not done and this is unlikely to happen because the >>> number of bytes associated to a meta page is going to be always >>> cheaper than a FPW, which would cost in CPU to store it for >>> compression is enabled. So I think that we should switch comments to >>> mention that pd_lower is set so as this helps with page masking, but >>> we don't take advantage of XLOG compression in the code. >>> >> >> I think that is not true because we do need FPW for certain usages of >> metapage. Consider a case in _hash_doinsert where register metabuf >> with just >> REGBUF_STANDARD, it can take advantage of removing the hole if >> pd_lower is set to its correct position. > > I am not saying that no index AMs take advantage FPW compressibility > for their meta pages. There are cases like this one, as well as one > code path in BRIN where this is useful, and it is useful as well when > logging FPWs of the init forks for unlogged relations. >
Hmm, why is it useful for logging FPWs of the init forks for unlogged relations? We don't use REGBUF_STANDARD in those cases. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
