ANTI-JOIN needs table, index scan not possible?

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От hans wulf
Тема ANTI-JOIN needs table, index scan not possible?
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Msg-id 20110311153205.6380@gmx.net
обсуждение исходный текст
Ответы Re: ANTI-JOIN needs table, index scan not possible?  (Maciek Sakrejda <msakrejda@truviso.com>)
Re: ANTI-JOIN needs table, index scan not possible?  (Robert Haas <robertmhaas@gmail.com>)
Список pgsql-performance
Hi,

I need an ANTI-JOIN (not exists SELECT something from table.../ left join table WHERE table.id IS NULL) on the same
table.Acutally I have an index to serve the not exists question, but the query planner chooses to to a bitmap heap
scan.

The table has 100 Mio rows, so doing a heap scan is messed up...

It would be really fast if Postgres could compare the to indicies. Does Postgres have to visit the table for this
ANTI-JOIN?

I know the table has to be visitied at some point to serve the MVCC, but why so early? Can NOT ESISTS only be fixed by
thetable, because it could miss soemthing otherwise? 

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