How to calculate the size of the undo tablespace In the undo Series

Source: Internet
Author: User

The undo series learn how to calculate the size of undo tablespaces undo space insufficiency can cause ORA-30036 or ORA-01555. We create a small undo tablespace and execute a large transaction, then we can simulate the ORA-30036. [SQL] sys @ ORCL> create undo tablespace thinktbs datafile '/u01/app/oracle/oradata/ORCL/datafile/think_undo.dbf' 2 size 2 m autoextend off; Tablespace created. sys @ ORCL> alter system set undo_tablespace = thinktbs; System altered. sys @ ORCL> show parameter undo name type value =----------- export undo_management string AUTO undo_retention integer 800 undo_tablespace string THINKTBS another session: hr @ ORCL> select count (*) from t; COUNT (*) ---------- 462140 hr @ ORCL> begin 2 for I in 1 .. 1000 3 loop 4 delete from t where rownum <1001; 5 commit; 6 end loop; 7 end; 8/begin * ERROR at line 1: ORA-30036: unable to extend segment by 8 in undo tablespace 'thinktbs 'ORA-06512: at line 4
During the execution of this transaction, we can query how many undo data blocks it uses: sys @ ORCL> select addr, used_ublk from v $ transaction; ADDR USED_UBLK -------- ---------- 37A19440 19 37A19E88 1 how should we determine the size of the undo tablespace? The size of the undo tablespace has three influencing factors: 1) undo_retention: determine the value. See: 2) undo data blocks required per second: We can query the value from v $ undostat to calculate the maximum value or average value, but we recommend that you set the maximum value to 3) default block size formula undo size = db_block_size * undo_retention * max (undoblks/(end_time-begin_time) * 24*3600 )) [SQL] sys @ ORCL> select max (undoblks/(end_time-begin_time) * 24*3600) from v $ undostat; MAX (UNDOBLKS/(END_TIME-BEGIN_TIME) * 24*3600) --------------------------------------------- 5.77333333 sys @ ORCL> show parameter db_block_size NAME Type value when ----------- mongodb_block_size integer 8192 sys @ ORCL> show parameter undo_retention name type value when ----------- using undo_retention integer 800 through the above query, we can calculate the specific VALUE of the undo tablespace size.. We can increase the size of the undo tablespace accordingly. [SQL] sys @ ORCL> alter tablespace undotbs1 add datafile '/u01/app/oracle/oradata/ORCL/datafile/thinkundo. dbf 'size 30 m autoextend on; Tablespace altered. author: linwaterbin

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