Foreign key creation is very slow

Question

Hello,
We are about to migrate a database from 9iR2 to 10g by doing export/import.
One of the last steps of the migration, after the import, is to create constraints and indexes. The foreign key creation process is lasting about 7 hours, and this is something we cannot afford. How could we speed up this process of foreign key creation?
Thanks in advance,
Eva

Answer 1

Look at the statement (using enterprise manager, SQL*Plus, sql trace or whatever) while the foreign keys are enabled/created. Basically for following tables:
SQL> create table big as select * from dba_source;
Table created.
SQL> create table big1 as select * from dba_source;
Table created.
SQL> alter table big add constraint big_pk primary key (owner, name, type, line, text);
Table altered.and following foreign key:
SQL> alter table big1 add constraint big1_big_fk
  2  foreign key (owner, name, type, line, text)
  3  references big (owner, name, type, line, text);the statement is:
select /*+ all_rows ordered */ A.rowid, :1, :2, :3
from
"GINTS"."BIG1" A , "GINTS"."BIG" B where( "A"."OWNER" is not null and
  "A"."NAME" is not null and "A"."TYPE" is not null and "A"."LINE" is not
  null and "A"."TEXT" is not null) and( "B"."OWNER" (+)= "A"."OWNER" and
  "B"."NAME" (+)= "A"."NAME" and "B"."TYPE" (+)= "A"."TYPE" and "B"."LINE" (+)
  = "A"."LINE" and "B"."TEXT" (+)= "A"."TEXT") and( "B"."OWNER" is null or
  "B"."NAME" is null or "B"."TYPE" is null or "B"."LINE" is null or
  "B"."TEXT" is null)As usually such statement can be executed using various execution plans. And as usual some are better than other for example I could manage 2 variants:
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.00       0.00          0          0          0           0
Execute      1      0.00       0.00          0          3          0           0
Fetch        1     59.48      74.29      77125   10217945          0           0
total        3     59.48      74.30      77125   10217948          0           0
Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: SYS   (recursive depth: 1)
Rows     Row Source Operation
      0  CONCATENATION  (cr=10217945 pr=77125 pw=0 time=74294598 us)
      0   FILTER  (cr=2043589 pr=15557 pw=0 time=16167973 us)
1014081    NESTED LOOPS OUTER (cr=2043589 pr=15557 pw=0 time=16234254 us)
1014081     TABLE ACCESS FULL BIG1 (cr=15425 pr=15265 pw=0 time=4065256 us)
1014081     INDEX UNIQUE SCAN BIG_PK (cr=2028164 pr=292 pw=0 time=10314886 us)(object id 125287)
      0   FILTER  (cr=2043589 pr=15331 pw=0 time=14522620 us)
1014081    NESTED LOOPS OUTER (cr=2043589 pr=15331 pw=0 time=16225336 us)
1014081     TABLE ACCESS FULL BIG1 (cr=15425 pr=15331 pw=0 time=4056358 us)
1014081     INDEX UNIQUE SCAN BIG_PK (cr=2028164 pr=0 pw=0 time=8736590 us)(object id 125287)
      0   FILTER  (cr=2043589 pr=15413 pw=0 time=15081218 us)
1014081    NESTED LOOPS OUTER (cr=2043589 pr=15413 pw=0 time=16257085 us)
1014081     TABLE ACCESS FULL BIG1 (cr=15425 pr=15413 pw=0 time=4087642 us)
1014081     INDEX UNIQUE SCAN BIG_PK (cr=2028164 pr=0 pw=0 time=9114281 us)(object id 125287)
      0   FILTER  (cr=2043589 pr=15412 pw=0 time=14470176 us)
1014081    NESTED LOOPS OUTER (cr=2043589 pr=15412 pw=0 time=16260121 us)
1014081     TABLE ACCESS FULL BIG1 (cr=15425 pr=15412 pw=0 time=4091125 us)
1014081     INDEX UNIQUE SCAN BIG_PK (cr=2028164 pr=0 pw=0 time=8833532 us)(object id 125287)
      0   FILTER  (cr=2043589 pr=15412 pw=0 time=14052583 us)
1014081    NESTED LOOPS OUTER (cr=2043589 pr=15412 pw=0 time=15224595 us)
1014081     TABLE ACCESS FULL BIG1 (cr=15425 pr=15412 pw=0 time=4069696 us)
1014081     INDEX UNIQUE SCAN BIG_PK (cr=2028164 pr=0 pw=0 time=8607611 us)(object id 125287)
Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file scattered read                       4906        0.12         13.62
  db file sequential read                       362        0.11          1.78and
call     count       cpu    elapsed       disk      query    current        rows
Parse        1      0.01       0.00          0          0          0           0
Execute      1      0.00       0.00          0          0          0           0
Fetch        1      4.57      23.10      22563      30850          0           0
total        3      4.59      23.11      22563      30850          0           0
Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: SYS   (recursive depth: 1)
Rows     Row Source Operation
      0  FILTER  (cr=30850 pr=22563 pw=0 time=23106976 us)
1014081   HASH JOIN OUTER (cr=30850 pr=22563 pw=0 time=20989057 us)
1014081    TABLE ACCESS FULL BIG1 (cr=15425 pr=10342 pw=0 time=6122826 us)
1014081    TABLE ACCESS FULL BIG (cr=15425 pr=12221 pw=0 time=4079771 us)
Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  db file scattered read                       4114        0.21         13.20
  db file sequential read                      1849        0.22          5.55Obviously the second one is about 2 times better than the first one.
So I'v managed to get it using:
1) dbms_stats to compute stats on these table so that Oracle understand that these are really large tables
2) altering session to use manual workarea size policy and give more resources for hash joins and sorts:
SQL> alter session set workarea_size_policy= manual;
Session altered.
Elapsed: 00:00:00.01
SQL> alter session set sort_area_size = 1000000000;
Session altered.
Elapsed: 00:00:00.01
SQL> alter session set hash_area_size = 1000000000;So the trick is - understand the bottleneck and trying to do something about it. In my case I cannot do much more because everything now is dependant on disks and I cannot make my pc much faster :)))
Another options is to create FKses either disabled and enable them later on or create enabled but not validate them. This is almost instantenous as you can see in the following code snippet. Of course that might give some implications later, especially if you create them disabled :)
SQL> alter table big1 add constraint big1_big_fk
  2  foreign key (owner, name, type, line, text)
  3  references big (owner, name, type, line, text)
  4  disable;
Table altered.
Elapsed: 00:00:00.03
SQL> alter table big1 drop constraint big1_big_fk;
Table altered.
Elapsed: 00:00:00.01
SQL> alter table big1 add constraint big1_big_fk
  2  foreign key (owner, name, type, line, text)
  3  references big (owner, name, type, line, text)
  4  enable novalidate;
Table altered.
Elapsed: 00:00:00.03
SQL> Gints Plivna
http://www.gplivna.eu