???Past Image(pi)
- by todd.bao(at)oracle.com
Past Image???RAC??????????,????????????????????????????????,Past Image??????????,?????????????????,?????????????????,??????????????(pi)?????????????????Past Image,????????????:HR.EMPLOYEES??100????101?????5????88???????????????,???????????# ??1: ?????????SYS@RAC1//scripts> select inst_id,status from gv$bh where file#=5 and block#=88;no rows selected# ??1???(???Steve King, ????24000????)SYS@RAC1//scripts> update hr.employees set salary=1 where employee_id=100;1 row updated.# ??2: ????1??xcur????????????,?????????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88; INST_ID + D + STATUS---------- + - + ------- 1 + Y + xcur1 row selected.# ??2???SYS@RAC2//scripts> update hr.employees set salary=2 where employee_id=101;1 row updated.# ??3: ????2?,?????1??pi??Past Image,???????????????????????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88; INST_ID + D + STATUS---------- + - + ------- 1 + Y + pi 2 + Y + xcur2 rows selected.# ??1???SYS@RAC1//scripts> update hr.employees set salary=3 where employee_id=100;1 row updated.# ??4: ????1?,?????2???1???????2???????1???????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88; INST_ID + D + STATUS---------- + - + ------- 1 + Y + pi 1 + Y + xcur 2 + Y + pi3 rows selected.# ??2????SYS@RAC2//scripts> update hr.employees set salary=4 where employee_id=101;1 row updated.# ??5: ????2?,??????????????,DBWR??,??????,??(pi)?????????????(cr)??????????????????????????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88; INST_ID + D + STATUS---------- + - + ------- 1 + N + cr 1 + N + cr 2 + Y + xcur3 rows selected.# ?????1???SYS@RAC1//scripts> update hr.employees set salary=5 where employee_id=100;1 row updated.# ??6: ????1?,?????2????????????????,?????????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88; INST_ID + D + STATUS---------- + - + ------- 1 + Y + xcur 1 + N + cr 1 + N + cr 2 + Y + pi4 rows selected.# ??2???SYS@RAC2//scripts> update hr.employees set salary=6 where employee_id=101;1 row updated.# ??7: ????2?,?????1?2????1???????2?????????????4,????????????????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88; INST_ID + D + STATUS---------- + - + ------- 1 + Y + pi 2 + Y + pi 2 + Y + xcur3 rows selected.# ??1???SYS@RAC1//scripts> update hr.employees set salary=7 where employee_id=100;1 row updated.# ??8: ????1?,?????2?1????2???????1????????????2????????????????????????????????????(????????)????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88; INST_ID + D + STATUS---------- + - + ------- 1 + Y + pi 1 + Y + xcur 2 + Y + pi 2 + N + cr4 rows selected.??????????, ?xcur??????????:??????xcur????pi?????pi?(?????)???cr?,???cr?????,pi????????????????????????????:?????????????A?B?A:SYS@RAC1//scripts> run 1 begin 2 for i in 1..100000 loop 3 update hr.employees set salary=i where employee_id=100; 4 end loop; 5* end;B:SYS@RAC2//scripts> run 1 begin 2 for i in 1..100000 loop 3 update hr.employees set salary=i where employee_id=101; 4 end loop; 5* end;?????????,???5???88?????buffer cache???????:SYS@RAC2//scripts> select count(*) from gv$bh where file#=5 and block#=88; COUNT(*)---------- 4121 row selected.??409?????????(cur):SYS@RAC2//scripts> select count(*) from gv$bh where file#=5 and block#=88 where status='cr'; COUNT(*)---------- 4091 row selected.1????????(xcur):SYS@RAC2//scripts> select count(*) from gv$bh where file#=5 and block#=88 where status='xcur'; COUNT(*)---------- 11 row selected.??...2??????--????(pi)??????????SYS@RAC1//scripts> select inst_id,dirty,status from gv$bh where file#=5 and block#=88 and status='pi'; INST_ID + D + STATUS---------- + - + ------- 1 + Y + pi 2 + Y + pi2 rows selected.????,???RAC??????????????(cr)?,????????????????????????xcur?pi??cr??????pi?????? ?????????,???????????pi???cr?,?????????cr???,???xcur???????,pi??????xcur?,[email protected]
