Re: RTREE Index on primary key generated by a sequence
От | Jean-Paul ARGUDO |
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Тема | Re: RTREE Index on primary key generated by a sequence |
Дата | |
Msg-id | 20020125155558.GA31304@pastis обсуждение исходный текст |
Ответ на | Re: RTREE Index on primary key generated by a sequence (Tom Lane <tgl@sss.pgh.pa.us>) |
Ответы |
Re: RTREE Index on primary key generated by a sequence
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Список | pgsql-hackers |
Tom, Since my english is not so fluent, I found on the net a little explication about Reverse Key Indexes (not RTREE, sorry :). As an explication, you could read there the point 9 : http://oracle.oreilly.com/news/oraclepp_0900.html Wich I copy here : « 9.Use Reverse Key Indexes. An index block typically references more rows than are contained in each data block for the corresponding table. When an index is based on a column that increases in a sequential fashion, and two or more instances are inserting data into the underlying table, there is a strong likelihood that both instances will be contending for the same index block. This is because sequential index entries are likely to be in the same block. Reverse key indexes reverse the bytes in each index entry, causing sequential entries to be dispersed across the index tree. Hence, there is less chance of contention for the same index block. One trade-off involved with using this technique is that by its nature, reverse key indexes cannot be used as the basis for an index range scan. » Thanks. -- Jean-Paul ARGUDO IDEALX S.A.S Consultant bases de données 15-17, av. de Ségur http://IDEALX.com/ F-75007 PARIS
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