Oracle技术：Oracleflashbackbuffer参数
我们知道在Oracle 10g中，如不美观数据库启用flashback功能，Oracle即在shared pool平分配flashback buffer，以下是Oracle部门启动日志，可以清嚣张的看到flashback buffer在shared pool分配了3981204 bytes。 引用Wed Dec 30 15:20:40 2009
Allocated 3981204 bytes in shared pool for flashback generation buffer
Starting background process RVWR
RVWR started with pid=16, OS id=724
同样在数据字典中也可以看到flashback buffer的巨细：
引用
SQL> select name,bytes from V$sgastat
2where pool=’shared pool’
3and name like ‘%flash%’;
NAME BYTES
————————– ———-
flashback generation buff 3981204
当flashback buffer空间严重时，可能会呈现flashback buf free by RVWR期待事务，Oracle并没有供给参数调节flashback buffer，对于高吞吐量，并发量系统初始巨细并不能知足系统要求
今朝系统中log_buffer巨细为7012352 bytes，将其改为10M，重启数据库，不雅察看flashback buffer转变。
引用
SQL> show parameter log_buffer
NAME TYPE VALUE
———————————— ———– ——————————
log_buffer integer 7012352
SQL> alter system set log_buffer=10000000 scope=spfile;
System altered.
SQL> select name,bytes from V$sgastat
2where pool=’shared pool’
3and name like ‘%flash%’;
NAME BYTES
—————————— ———-
flashback generation buff 3981204
SQL> startup force
ORACLE instance started.
Oracle技术：Oracleflashbackbuffer参数
</p> Total System Global Area536870912 bytesFixed Size 1262764 bytes
Variable Size 155192148 bytes
Database Buffers 369098752 bytes
Redo Buffers 11317248 bytes
Database mounted.
Database opened.
SQL> select name,bytes from V$sgastat
2where pool=’shared pool’
3and name like ‘%flash%’;
NAME BYTES
—————————— ———-
flashback generation buff 3981204
可以看到flashback generation buff巨细并没有发生转变。
进一步，不雅察看和flashback相关的隐含参数
引用
SQL> set linesize 120
SQL> col name for a40 trunc
SQL> col value for a20
SQL> col pdesc for a50 trunc
SQL> SELECT x.ksppinm NAME, y.ksppstvl VALUE, x.KSPPDESC PDESC
2 FROM SYS.x$ksppi x, SYS.x$ksppcv y
3WHERE x.indx = y.indx AND x.ksppinm LIKE ‘%&par%’;
Enter value for par: flashback
old 3: WHERE x.indx = y.indx AND x.ksppinm LIKE ‘%&par%’
new 3: WHERE x.indx = y.indx AND x.ksppinm LIKE ‘%flashback%’
NAME VALUE PDESC
—————————————- ——————– ————————————————–
Oracle技术：Oracleflashbackbuffer参数
</p> db_flashback_retention_target 1440 Maximum Flashback Database log retention time in m_validate_flashback_database FALSE Scan database to validate result of flashback data
_flashback_allow_noarchivelog FALSE Allow enabling flashback on noarchivelog database
_verify_flashback_redo TRUE Verify that the redo logs needed for flashback are
_flashback_verbose_info FALSE Print verbose information about flashback database
_flashback_logfile_enqueue_timeout 600 flashback logfile enqueue timeout for opens
_flashback_barrier_interval 1800 Flashback barrier interval in seconds
_flashback_standby_barrier_interval 1800 Flashback standby barrier interval in seconds
_flashback_fuzzy_barrier TRUE Use flashback fuzzy barrier
_flashback_log_size 1000 Flashback log size
_flashback_log_min_size 100 Minimum flashback log size
NAME VALUE PDESC
—————————————- ——————– ————————————————–
_flashback_copy_latches 10 Number of flashback copy latches
_flashback_n_log_per_thread 128 Desired number of flashback logs per flashback thr
_flashback_max_n_log_per_thread 2048 Maximum number of flashback logs per flashback thr
_flashback_generation_buffer_size 134193152 flashback generation buffer size
_flashback_max_log_size 0 Maximum flashback log size in bytes (OS limit)
_flashback_log_io_error_behavior 0 Specify Flashback log I/O error behavior
_flashback_hint_barrier_percent 20 Flashback hint barrier percent
_percent_flashback_buf_partial_full 50 Percent of flashback buffer filled to be considere
_flashback_write_size_qm 4 Desired flashback write size in quarter MB
20 rows selected.
调节隐含参数_flashback_generation_buffer_size，可以看到flashback generation buff 并没有发生转变。
页:
[1]