Re: Hash index todo list item
От | Hannu Krosing |
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Тема | Re: Hash index todo list item |
Дата | |
Msg-id | 1189087192.7470.16.camel@hannu-laptop обсуждение исходный текст |
Ответ на | Re: Hash index todo list item (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: Hash index todo list item
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Список | pgsql-hackers |
Ühel kenal päeval, N, 2007-09-06 kell 09:38, kirjutas Tom Lane: > Hannu Krosing <hannu@skype.net> writes: > > Ühel kenal päeval, E, 2007-09-03 kell 19:55, kirjutas Tom Lane: > >> No, because part of the deal is that you can do lookups using only the > >> leading index columns. At least, all the existing multicolumn index > >> types can do that. > > > One approahc is not to mix hashes, but to partition the hash, so that > > each column gets its N bits in the hash. > > How does that help? You still need all the keys to find out which > bucket to look in. no. you need to look at only the buckets where that part of hash matches say you allocate bits 4-7 for column 2 and then need to look up column 2 value with hash 3 . here you need to look at only buckets N*16 + 3, that is, you need to examine only each 16th bucket --------- Hannu
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