Re: How are foreign key constraints built?
От | Jim C. Nasby |
---|---|
Тема | Re: How are foreign key constraints built? |
Дата | |
Msg-id | 20050123215923.GB67721@decibel.org обсуждение исходный текст |
Ответ на | Re: How are foreign key constraints built? (Alvaro Herrera <alvherre@dcc.uchile.cl>) |
Список | pgsql-general |
On Sun, Jan 23, 2005 at 06:45:36PM -0300, Alvaro Herrera wrote: > On Sun, Jan 23, 2005 at 03:19:10PM -0600, Jim C. Nasby wrote: > > > > People have this weird notion that an index-based plan is always faster > > > than anything else. If you like you can try the operation with "set > > > enable_seqscan = off", but I bet it will take longer. > > > > Well, every other database I've used can do index covering, which means > > index scans *are* faster. > > ... on those database systems. Indexes are different in Postgres in > general: they don't have visibility info (other systems don't need it, > tuples are always visible), and in some databases you have clustered > indexes, where the index is also the heap. Yes, I understand. I was just pointing out that in other databases, an index scan of even the entire table can be faster, hence the mentality that index scans are always better. I really hope that the current discussion on hackers about tuple visibility in indexes leads somewhere; I think that would be a huge gain for PostgreSQL. -- Jim C. Nasby, Database Consultant decibel@decibel.org Give your computer some brain candy! www.distributed.net Team #1828 Windows: "Where do you want to go today?" Linux: "Where do you want to go tomorrow?" FreeBSD: "Are you guys coming, or what?"
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