Re: Constant time insertion into highly non-unique
От | Simon Riggs |
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Тема | Re: Constant time insertion into highly non-unique |
Дата | |
Msg-id | 1113494116.16721.1916.camel@localhost.localdomain обсуждение исходный текст |
Ответ на | Re: Constant time insertion into highly non-unique indexes (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-hackers |
On Thu, 2005-04-14 at 11:15 -0400, Tom Lane wrote: > Simon Riggs <simon@2ndquadrant.com> writes: > > The move right only occurs when the page is full, so the chance of > > moving right is not 0.99^250, but 0.99, since the previous 249 inserts > > would not cause a page split. > > Sure, but given that we have a full page, the probability that 250 > successive insertions *all* decide to move right rather than split > that page is 0.99^250. And it only takes one decision to split to > maintain the constant-time behavior. So I still think your analysis > is incorrect. OK... point accepted. Darn, but also thank goodness it performs. P(N) > 0.999 for W byte keys, at... N W Mean blocks read/insert 3 4 bytes 1.1 5 8 bytes 1.4 11 16 bytes 2.1 22 32 bytes 3.6 43 64 bytes 6.7 83 128 bytes 12.5 lots 256 bytes 23 > > IMHO the performance figures show this to be true. > > *What* performance figures? The figures shown on PERFORM recently, with graphs. We still have a performance issue with insertion rate for large indexes. Best Regards, Simon Riggs
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