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IDS Forum

Re: Update stats impacts insert performance

Posted By: HOWARD ANDERSON
Date: Friday, 21 August 2009, at 6:51 a.m.

In Response To: Re: Update stats impacts insert performance (Art Kagel)

Art,

Many thanks for the prompt reply,

I enclose a snippet of the schema dump for this table, showing the index definitions.
As you can see a primary key is defined on multiple columns, but I know of no other 'hidden' index constraints.

Thanks for the link to John's paper, I had already read this, and was running some tests using the PDQ environment variables, but I did not see much (if any) gain. Possibly this is due to insufficent available physicial memory on the system. 'Set explain' showed that the sort data was 32Gb for HIGH, and 41Mb was available when PDQ was enabled. I only have 4Gb of physical memory installed, and much of this has already been devoured by the database. I also only have 2 processors in this system, so PSORT_NPROCS is only set to 2. I am going to set DBUPSPACE=0:50:0 as this gives 50Mb.

Chuck Berghoff also mentioned use of PDQ to utilise the Memory Grant Manager, and mentions PSORT_DBSPACE, which I have not yet tried, as I have DBSPACETEMP set in onconfig, however it may be worth trying PSORT_DBSPACE to override this, just for the update stats. I am using a Compaq ES40 Alphaserver and this would seem comparable to his Sun V490, however he is using V10.00.FC5, and this may be giving an improvement. (I cannot upgrade on my current hardware.)

I will download a copy of your dostats utility and give it a try.

A colleauge on an internal company forum pointed out to me that each week only a very small percentage of the data in the table has changed, (1bn to 1.001bn) so a weekly frequency for update sats on this table is too high. He has suggested that a biannual frequency may be more appropriate. My only concern with this is that it could still impact performance at that point. The root problem is the performance impact on insertion. Is it possible to 'nice' the update stats process in some way ? (Reduce its use of system resorces, at the expense of time taken.)

Would setting a 'DIRTY READ' isolation level have any performance benefit ? Or would this just produce inaccurate stats ?

Schema dump:
(I have obfuscated the folowing somewhat, as I don't want to expose the real table or column names.)

{ TABLE "informix".xxx row size = 122 number of columns = 12 index size = 70

}
create table "informix".xxx
(

aaa varchar(12),

bbb datetime year to second,

ccc char(2),

eee char(1),

fff char(2),

ggg char(2),

hhh smallint,

iii integer,

jjj char(2),

kkk varchar(80),

lll char(1),

ddd serial not null ,

check (lll IN ('Y' ,'N' ))
)
fragment by expression

((MONTH (bbb ) = 1 ) AND (DAY (bbb ) <= 15 )

) in fragm001 ,

((MONTH (bbb ) = 1 ) AND (DAY (bbb ) > 15 ) )

in fragm002 ,

((MONTH (bbb ) = 2 ) AND (DAY (bbb ) <= 15 )

) in fragm003 ,

((MONTH (bbb ) = 2 ) AND (DAY (bbb ) > 15 ) )

in fragm004 ,

((MONTH (bbb ) = 3 ) AND (DAY (bbb ) <= 15 )

) in fragm005 ,

((MONTH (bbb ) = 3 ) AND (DAY (bbb ) > 15 ) )

in fragm006 ,

((MONTH (bbb ) = 4 ) AND (DAY (bbb ) <= 15 )

) in fragm007 ,

((MONTH (bbb ) = 4 ) AND (DAY (bbb ) > 15 ) )

in fragm008 ,

((MONTH (bbb ) = 5 ) AND (DAY (bbb ) <= 15 )

) in fragm009 ,

((MONTH (bbb ) = 5 ) AND (DAY (bbb ) > 15 ) )

in fragm010 ,

((MONTH (bbb ) = 6 ) AND (DAY (bbb ) <= 15 )

) in fragm011 ,

((MONTH (bbb ) = 6 ) AND (DAY (bbb ) > 15 ) )

in fragm012 ,

((MONTH (bbb ) = 7 ) AND (DAY (bbb ) <= 15 )

) in fragm013 ,

((MONTH (bbb ) = 7 ) AND (DAY (bbb ) > 15 ) )

in fragm014 ,

((MONTH (bbb ) = 8 ) AND (DAY (bbb ) <= 15 )

) in fragm015 ,

((MONTH (bbb ) = 8 ) AND (DAY (bbb ) > 15 ) )

in fragm016 ,

((MONTH (bbb ) = 9 ) AND (DAY (bbb ) <= 15 )

) in fragm017 ,

((MONTH (bbb ) = 9 ) AND (DAY (bbb ) > 15 ) )

in fragm018 ,

((MONTH (bbb ) = 10 ) AND (DAY (bbb ) <= 15 )

) in fragm019 ,

((MONTH (bbb ) = 10 ) AND (DAY (bbb ) > 15 )

) in fragm020 ,

((MONTH (bbb ) = 11 ) AND (DAY (bbb ) <= 15 )

) in fragm021 ,

((MONTH (bbb ) = 11 ) AND (DAY (bbb ) > 15 )

) in fragm022 ,

((MONTH (bbb ) = 12 ) AND (DAY (bbb ) <= 15 )

) in fragm023 ,

((MONTH (bbb ) = 12 ) AND (DAY (bbb ) > 15 )

) in fragm024
extent size 128000 next size 128000 lock mode row;
revoke all on "informix".xxx from "public";

create unique index "informix".ix_x_aaa on "informix".xxx

(aaa,bbb,ccc)
fragment by expression

(aaa [1,1] <= 'A' ) in fragm001 ,

(aaa [1,1] = 'B' ) in fragm002 ,

(aaa [1,1] = 'C' ) in fragm003 ,

(aaa [1,1] = 'D' ) in fragm004 ,

(aaa [1,1] = 'E' ) in fragm005 ,

(aaa [1,1] = 'F' ) in fragm006 ,

(aaa [1,1] = 'G' ) in fragm007 ,

(aaa [1,1] = 'H' ) in fragm008 ,

(aaa [1,1] = 'I' ) in fragm009 ,

(aaa [1,1] = 'J' ) in fragm010 ,

(aaa [1,1] = 'K' ) in fragm011 ,

(aaa [1,1] = 'L' ) in fragm012 ,

(aaa [1,1] = 'M' ) in fragm013 ,

(aaa [1,1] = 'N' ) in fragm014 ,

(aaa [1,1] = 'O' ) in fragm015 ,

(aaa [1,1] IN ('P' ,'Q' )) in fragm016 ,

(aaa [1,1] = 'R' ) in fragm017 ,

(aaa [1,1] = 'S' ) in fragm018 ,

(aaa [1,1] = 'T' ) in fragm019 ,

(aaa [1,1] = 'U' ) in fragm020 ,

(aaa [1,1] = 'V' ) in fragm021 ,

(aaa [1,1] = 'W' ) in fragm022 ,

(aaa [1,1] = 'X' ) in fragm023 ,

(aaa [1,1] >= 'Y' ) in fragm024 ;

create index "informix".ix_x_bbb on "informix".xxx (bbb)

fragment by expression

((MONTH (bbb ) = 1 ) AND (DAY (bbb ) <= 15 )

) in fragm001 ,

((MONTH (bbb ) = 1 ) AND (DAY (bbb ) > 15 ) )

in fragm002 ,

((MONTH (bbb ) = 2 ) AND (DAY (bbb ) <= 15 )

) in fragm003 ,

((MONTH (bbb ) = 2 ) AND (DAY (bbb ) > 15 ) )

in fragm004 ,

((MONTH (bbb ) = 3 ) AND (DAY (bbb ) <= 15 )

) in fragm005 ,

((MONTH (bbb ) = 3 ) AND (DAY (bbb ) > 15 ) )

in fragm006 ,

((MONTH (bbb ) = 4 ) AND (DAY (bbb ) <= 15 )

) in fragm007 ,

((MONTH (bbb ) = 4 ) AND (DAY (bbb ) > 15 ) )

in fragm008 ,

((MONTH (bbb ) = 5 ) AND (DAY (bbb ) <= 15 )

) in fragm009 ,

((MONTH (bbb ) = 5 ) AND (DAY (bbb ) > 15 ) )

in fragm010 ,

((MONTH (bbb ) = 6 ) AND (DAY (bbb ) <= 15 )

) in fragm011 ,

((MONTH (bbb ) = 6 ) AND (DAY (bbb ) > 15 ) )

in fragm012 ,

((MONTH (bbb ) = 7 ) AND (DAY (bbb ) <= 15 )

) in fragm013 ,

((MONTH (bbb ) = 7 ) AND (DAY (bbb ) > 15 ) )

in fragm014 ,

((MONTH (bbb ) = 8 ) AND (DAY (bbb ) <= 15 )

) in fragm015 ,

((MONTH (bbb ) = 8 ) AND (DAY (bbb ) > 15 ) )

in fragm016 ,

((MONTH (bbb ) = 9 ) AND (DAY (bbb ) <= 15 )

) in fragm017 ,

((MONTH (bbb ) = 9 ) AND (DAY (bbb ) > 15 ) )

in fragm018 ,

((MONTH (bbb ) = 10 ) AND (DAY (bbb ) <= 15 )

) in fragm019 ,

((MONTH (bbb ) = 10 ) AND (DAY (bbb ) > 15 )

) in fragm020 ,

((MONTH (bbb ) = 11 ) AND (DAY (bbb ) <= 15 )

) in fragm021 ,

((MONTH (bbb ) = 11 ) AND (DAY (bbb ) > 15 )

) in fragm022 ,

((MONTH (bbb ) = 12 ) AND (DAY (bbb ) <= 15 )

) in fragm023 ,

((MONTH (bbb ) = 12 ) AND (DAY (bbb ) > 15 )

) in fragm024 ;

create index "informix".ix_x_ddd on "informix".xxx (ddd)
fragment by expression

(mod(ddd , 10 ) = 0 ) in fragm010 ,

(mod(ddd , 10 ) = 1 ) in fragm011 ,

(mod(ddd , 10 ) = 2 ) in fragm012 ,

(mod(ddd , 10 ) = 3 ) in fragm013 ,

(mod(ddd , 10 ) = 4 ) in fragm014 ,

(mod(ddd , 10 ) = 5 ) in fragm015 ,

(mod(ddd , 10 ) = 6 ) in fragm016 ,

(mod(ddd , 10 ) = 7 ) in fragm017 ,

(mod(ddd , 10 ) = 8 ) in fragm018 ,

(mod(ddd , 10 ) = 9 ) in fragm019 ;

alter table "informix".xxx add constraint primary key (aaa,

bbb,ccc) ;

Regards,

Howard Anderson

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