| From: | Leon <leon(at)udmnet(dot)ru> |
|---|---|
| To: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>, David Warnock <david(at)sundayta(dot)co(dot)uk>, pgsql-general <pgsql-general(at)postgreSQL(dot)org> |
| Subject: | Re[4]: [GENERAL] Joins and links |
| Date: | 1999-07-05 19:32:47 |
| Message-ID: | 322.990706@udmnet.ru |
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| Thread: | |
| Lists: | pgsql-general pgsql-hackers |
Hello Bruce,
Tuesday, July 06, 1999 you wrote:
>>
>> Maybe it is a silly question, but what are "more than one version
>> of a record"? In my opinion record is a atomic unique entity.
>> Isn't it?
B> Read how MVCC works in the manuals.
Ah, you mean MVCC! That's what I replied to Tom Lane:
> This problem can be solved. An offhand solution is to have
> an additional system field which will point to new tuple left after
> update. It is filled at the same time as the original tuple is
> marked invalid. So the scenario is as follows: we follow the link,
> and if we find that in the tuple where we arrived this system field
> is not NULL, we go to (the same table of course) where it is pointing
> to. Sure VACUUM will eliminate these. Performance penalty is small.
Best regards, Leon
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