How to gather statistics

Question

Hi folks!
I gathered statistcs in one schema with folowing options:
exec dbms_stats.gather_schema_stats(user,method_opt=>'FOR ALL COLUMNS SIZE 1',estimate_percent=>null,gather_temp=>false,cascade=>true,degree=>dbms_stats.auto_degree);Then:
exec dbms_stats.gather_schema_stats(user,method_opt=>'FOR ALL COLUMNS SIZE SKEWONLY',estimate_percent=>null,gather_temp=>false,cascade=>true,degree=>dbms_stats.auto_degree);Now, I turn on table monitoring and suggest to gather statistics (per day) with that parameters:
dbms_stats.gather_schema_stats(ownname =>user, options=>'GATHER STALE', gather_temp => false, cascade => true, estimate_percent => 100, degree => dbms_stats.auto_degree);Default method_opt is FOR ALL COLUMNS SIZE AUTO.
Now I got better perfomance. How often I need to gather statstics?
Thanks in advance.
Best regards, Pavel.

Answer 1

Thanks, I also think so.
Little test-case:
SQL>exec dbms_stats.gather_table_stats(user,'TABLE1',estimate_percent=>null);
Elapsed: 00:00:01.03
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE1;
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
DISGRP                                                                                             7944        33204
DISMBR                                                                                            18948        33204
TYPE                                                                                                  4        33204
Elapsed: 00:00:00.03
SQL> exec dbms_stats.gather_table_stats(user,'TABLE1',estimate_percent=>10);
PL/SQL procedure successfully completed.
Elapsed: 00:00:01.78
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE1';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
DISGRP                                                                                             3836         3269
DISMBR                                                                                            13686         3269
TYPE                                                                                                  4         3269
Elapsed: 00:00:00.00
SQL> exec dbms_stats.gather_table_stats(user,'TABLE1',estimate_percent=>100);
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.52
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE1';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
DISGRP                                                                                             7944        33204
DISMBR                                                                                            18948        33204
TYPE                                                                                                  4        33204
Elapsed: 00:00:00.01
SQL> exec dbms_stats.gather_table_stats(user,'TABLE1',estimate_percent=>dbms_stats.auto_sample_size);
PL/SQL procedure successfully completed.
Elapsed: 00:00:00.53
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE1';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
DISGRP                                                                                             8448         5568
DISMBR                                                                                            18948        33204
TYPE                                                                                                  4         5568
Elapsed: 00:00:00.00
SQL> select count(distinct disgrp) from TABLE1;
COUNT(DISTINCTDISGRP)
                 7944
Elapsed: 00:00:00.02
SQL> select count(distinct dismbr) from TABLE1;
COUNT(DISTINCTDISMBR)
                18948
Elapsed: 00:00:00.03
SQL> select count(distinct type) from TABLE1;
COUNT(DISTINCTTYPE)
                  4
Elapsed: 00:00:00.01
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE2';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
ID                                                                                               219120       219120
UNIT                                                                                             114762       219120
LOC                                                                                                  61       219120
TIS                                                                                                1230       219120
RTYP                                                                                                  3       219120
Elapsed: 00:00:00.02
SQL> exec dbms_stats.gather_table_stats(user,'TABLE2',estimate_percent=>null);
PL/SQL procedure successfully completed.
Elapsed: 00:00:07.61
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE2';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
ID                                                                                               219120       219120
UNIT                                                                                             114762       219120
LOC                                                                                                  61       219120
TIS                                                                                                1230       219120
RTYP                                                                                                  3       219120
Elapsed: 00:00:00.00
SQL> exec dbms_stats.gather_table_stats(user,'TABLE2',estimate_percent=>10);
PL/SQL procedure successfully completed.
Elapsed: 00:00:02.90
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE2';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
ID                                                                                               219950        21995
UNIT                                                                                              70812        21995
LOC                                                                                                  43        21995
TIS                                                                                                 496        21995
RTYP                                                                                                  3        21995
Elapsed: 00:00:00.00
SQL> exec dbms_stats.gather_table_stats(user,'TABLE2',estimate_percent=>50);
PL/SQL procedure successfully completed.
Elapsed: 00:00:03.70
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE2';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
ID                                                                                               218716       109358
UNIT                                                                                              92338       109426
LOC                                                                                                  61       109455
TIS                                                                                                 994       109567
RTYP                                                                                                  3       109422
Elapsed: 00:00:00.00
SQL> exec dbms_stats.gather_table_stats(user,'COMPS',estimate_percent=>100);
PL/SQL procedure successfully completed.
Elapsed: 00:00:04.37
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE2';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
ID                                                                                               219120       219120
UNIT                                                                                             114762       219120
LOC                                                                                                  61       219120
TIS                                                                                                1230       219120
RTYP                                                                                                  3       219120
Elapsed: 00:00:00.00
SQL> exec dbms_stats.gather_table_stats(user,'COMPS',estimate_percent=>dbms_stats.auto_sample_size);
PL/SQL procedure successfully completed.
Elapsed: 00:00:03.81
SQL> select column_name,num_distinct,sample_size from user_tab_col_statistics where table_name='TABLE2';
COLUMN_NAME                                                                                NUM_DISTINCT  SAMPLE_SIZE
ID                                                                                               217968        54492
UNIT                                                                                             122237        54492
LOC                                                                                                  31         5495
TIS                                                                                                 240         5495
RTYP                                                                                                  3         5495
Elapsed: 00:00:00.01
SQL> select count(distinct id) from TABLE2;
COUNT(DISTINCTID)
           219120
Elapsed: 00:00:00.27
SQL> select count(distinct unit) from TABLE2;
COUNT(DISTINCTUNIT)
             114762
Elapsed: 00:00:00.30
SQL> select count(distinct loc) from TABLE2;
COUNT(DISTINCTLOC)
                61
Elapsed: 00:00:00.06
SQL> select count(distinct tis) from TABLE2;
COUNT(DISTINCTTIS)
              1230
Elapsed: 00:00:00.09In that situation, auto_sample_size not bad? But estimate_percent=>100 - exact.
Best regards, Pavel.