Re: SELECT INTO large FKyed table is slow - Mailing list 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
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