| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, "Wood, Dan" <hexpert(at)amazon(dot)com>, pgsql-committers <pgsql-committers(at)postgresql(dot)org>, "Wong, Yi Wen" <yiwong(at)amazon(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple |
| Date: | 2017-11-10 00:45:07 |
| Message-ID: | CAH2-WzkXq0iNHVr8uLntaHk080u=gu40jg8rihFsRKUTLST8vQ@mail.gmail.com |
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| Lists: | pgsql-committers pgsql-hackers |
On Thu, Nov 9, 2017 at 4:17 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> Actually, on second thought, I take that back -- I don't think that
>> REINDEXing will even finish once a HOT chain is broken by the bug.
>> IndexBuildHeapScan() actually does quite a good job of making sure
>> that HOT chains are sane, which is how the enhanced amcheck notices
>> the bug here in practice.
>
> I think that's too optimistic.
Why? Because the "find the TID of the root" logic in
IndexBuildHeapScan()/heap_get_root_tuples() won't reliably find the
actual root (it might be some other HOT chain root following TID
recycling by VACUUM)?
Assuming that's what you meant: I would have thought that the
xmin/xmax matching within heap_get_root_tuples() makes the sanity
checking fairly reliable in practice.
--
Peter Geoghegan
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