Re: Amcheck: do rightlink verification with lock coupling
От | Tomas Vondra |
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Тема | Re: Amcheck: do rightlink verification with lock coupling |
Дата | |
Msg-id | 20200111122501.rhpxt5f44jlnee5u@development обсуждение исходный текст |
Ответ на | Re: Amcheck: do rightlink verification with lock coupling (Peter Geoghegan <pg@bowt.ie>) |
Ответы |
Re: Amcheck: do rightlink verification with lock coupling
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Список | pgsql-hackers |
On Fri, Jan 10, 2020 at 06:49:33PM -0800, Peter Geoghegan wrote: >On Fri, Jan 10, 2020 at 5:45 PM Tomas Vondra ><tomas.vondra@2ndquadrant.com> wrote: >> Peter, any opinion on this proposed amcheck patch? In the other thread >> [1] you seemed to agree this is worth checking, and Alvaro's proposal to >> make this check optional seems like a reasonable compromise with respect >> to the locking. > >It's a good idea, and it probably doesn't even need to be made >optional -- lock coupling to the right is safe on a primary, and >should also be safe on standbys (though I should triple check the REDO >routines to be sure). The patch only does lock coupling when it proves >necessary, which ought to only happen when there is a concurrent page >split, which ought to be infrequent. Maybe there is no need to >compromise. > OK, that makes sense. >I'm curious why Andrey's corruption problems were not detected by the >cross-page amcheck test, though. We compare the first non-pivot tuple >on the right sibling leaf page with the last one on the target page, >towards the end of bt_target_page_check() -- isn't that almost as good >as what you have here in practice? I probably would have added >something like this myself earlier, if I had reason to think that >verification would be a lot more effective that way. > >To be clear, I believe that Andrey wrote this patch for a reason -- I >assume that it makes a noticeable and consistent difference. I would >like to gain a better understanding of why that was for my own >benefit, though. For example, it might be that page deletion was a >factor that made the test I mentioned less effective. I care about the >specifics. > Understood. Is that a reason to not commit of this patch now, though? regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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