substring implementation (long string)
От | Scott Cain |
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Тема | substring implementation (long string) |
Дата | |
Msg-id | 1059533356.1545.65.camel@localhost.localdomain обсуждение исходный текст |
Ответы |
Re: substring implementation (long string)
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Список | pgsql-general |
Hello, I am wondering about the implementation of substring for very large strings. I've got strings that are several million characters long and frequently need to extract relatively small substrings (5000-40000 characters) (that's right, it's DNA). Before I cared much about performance, I retrieved the whole string and and substr'ed it in perl. I realized recently it is better to do the substring in postgres (performance increase by an order of magnitude). So here is what I am wondering: does postgres read the whole string into memory before it does the substring, or does it have some sort of smart way of reading just the substring from disk? I am wondering because I can think of ways of potentially improving performance, but at significant cost to the API, and I don't want to implement it unless I will get a big boost in performance. Thanks, Scott -- ------------------------------------------------------------------------ Scott Cain, Ph. D. cain@cshl.org GMOD Coordinator (http://www.gmod.org/) 216-392-3087 Cold Spring Harbor Laboratory
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