| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Qingqing Zhou <zhouqq(dot)postgres(at)gmail(dot)com> |
| Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Tuple visibility within a single XID |
| Date: | 2015-04-08 14:02:35 |
| Message-ID: | 4903.1428501755@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Qingqing Zhou <zhouqq(dot)postgres(at)gmail(dot)com> writes:
> Not sure if I understand correctly: in uniqueness check, we see all
> possible tuples with a dirty snapshot. For a tuple version inserted
> and updated by myself, it is surely dead no matter how the transaction
> ends. So I interpret that we can safely pruning the version.
It may be dead in the future, but unless you can prove that your session
does not still contain a snapshot that could "see" the row, you can't
prune it. Considering only the current query is a fundamental error.
regards, tom lane
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