dbms_stats.gather_table_stats和analyze table的一点细小差别
2008-12-01 11:03
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SQL> select * from v$version; BANNER ---------------------------------------------------------------- Oracle9i Enterprise Edition Release 9.2.0.4.0 - 64bit Production PL/SQL Release 9.2.0.4.0 - Production CORE 9.2.0.3.0 Production TNS for Solaris: Version 9.2.0.4.0 - Production NLSRTL Version 9.2.0.4.0 - Production SQL> create table t_test3 as select * from dba_tables; Table created. SQL> analyze table t_test3 compute statistics; Table analyzed. SQL> select avg_row_len,num_rows,blocks from user_tables where table_name = 'T_TEST3'; AVG_ROW_LEN NUM_ROWS BLOCKS ----------- ---------- ---------- 188 5502 146 SQL> analyze table t_test3 delete statistics; Table analyzed. SQL> exec dbms_stats.gather_table_stats(user,'T_TEST3'); PL/SQL procedure successfully completed. SQL> select avg_row_len,num_rows,blocks from user_tables where table_name = 'T_TEST3'; AVG_ROW_LEN NUM_ROWS BLOCKS ----------- ---------- ---------- 183 5502 146 SQL> 默认dbms_stats.gather_table_stats分析表得到平均行长貌视少一些。 SQL> create table t_test4 as select * from t_test3; Table created. SQL> exec dbms_stats.gather_table_stats(user,'T_TEST4',estimate_percent=>100); PL/SQL procedure successfully completed. SQL> select avg_row_len,num_rows,blocks from user_tables where table_name = 'T_TEST4'; AVG_ROW_LEN NUM_ROWS BLOCKS ----------- ---------- ---------- 183 5502 146 SQL> dbms_stats.gather_table_stats的输入参数estimate_percent为100(即100%评估),分析表得到平均行长就是准确了。 --End-- SELECT num_rows,blocks,empty_blocks as empty, avg_space, chain_cnt, avg_row_len FROM dba_tables WHERE owner = 'TEST' AND table_name = 'TEST1'; |
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