Re: SELECT INTO large FKyed table is slow
От | Mladen Gogala |
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Тема | Re: SELECT INTO large FKyed table is slow |
Дата | |
Msg-id | 4CF678FC.9050003@vmsinfo.com обсуждение исходный текст |
Ответ на | Re: SELECT INTO large FKyed table is slow (Mario Splivalo <mario.splivalo@megafon.hr>) |
Ответы |
Re: SELECT INTO large FKyed table is slow
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Список | pgsql-performance |
Mario Splivalo wrote: <blockquote cite="mid:4CF5FF0A.9040605@megafon.hr" type="cite"><br /><pre wrap=""> Yes, as Mladen Gogala had advised. No noticable change in performance - it's still slow :) </pre></blockquote><br /> Declaring constraints as deferrable doesn't do anything as such, you have toactually set the constraints deferred to have an effect. You have to do it within a transaction block. If done outsideof the transaction block, there is no effect:<br /><br /> This is what happens when "set constraints" is issued outsidethe transaction block:<br /><br /><blockquote>< constraint test1_pk primary key(col1) deferrable); <br/> NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "test1_pk" for table "test1"<br /> CREATE TABLE<br />Time: 41.218 ms<br /> scott=# set constraints all deferred; <br /> SET CONSTRAINTS<br /> Time:0.228 ms<br /> scott=# begin; <br /> BEGIN<br /> Time: 0.188 ms<br /> scott=# insert into test1 values(1); <br /> INSERT 0 1<br /> Time: 0.929 ms<br /> scott=# insert into test1values(1); <br /> ERROR: duplicate key value violates unique constraint "test1_pk"<br /> DETAIL: Key (col1)=(1)already exists.<br /> scott=# end;<br /> ROLLBACK<br /> Time: 0.267 ms<br /> scott=# <br /><br /></blockquote>It works like a charm when issued within the transaction block:<br /><blockquote>scott=# begin; <br /> BEGIN<br /> Time: 0.202 ms<br /> scott=# set constraints all deferred; <br /> SETCONSTRAINTS<br /> Time: 0.196 ms<br /> scott=# insert into test1 values(1); <br /> INSERT 0 1<br /> Time: 0.334 ms<br/> scott=# insert into test1 values(1); <br /> INSERT 0 1<br /> Time: 0.327 ms<br /> scott=# end;<br /> ERROR: duplicatekey value violates unique constraint "test1_pk"<br /> DETAIL: Key (col1)=(1) already exists.<br /> scott=# <br/></blockquote> I was able to insert the same value twice, it only failed at the end of the transaction.<br /><blockquotecite="mid:4CF5FF0A.9040605@megafon.hr" type="cite"><pre wrap=""> But, just for the sake of clarification - I tought that DEFERRABLE would matter if I do a lot of INSERTs, inside a FOR loop or something like that. Since I'm doing INSERT INTO ... SELECT, does it makes any difference? </pre></blockquote> You cannot tell which parttakes a long time, select or insert, without profiling. I certainly cannot do it over the internet.<br /><br /><pre class="moz-signature"cols="72">-- Mladen Gogala Sr. Oracle DBA 1500 Broadway New York, NY 10036 (212) 329-5251 <a class="moz-txt-link-freetext" href="http://www.vmsinfo.com">http://www.vmsinfo.com</a> The Leader in Integrated Media Intelligence Solutions </pre>
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