[20200309]数据库异常关闭恢复的终点.txt

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[20200309]数据库异常关闭恢复的终点.txt --//在链接:http://blog.itpub.net/267265/viewspace-2638170/=>[20190312]关于增量检查点的疑问(补充).txt --//我在里面提到数据库异常关闭恢复的起点是low_rba到on_disk_rba作为恢复终点. --//实际上可能更新这些信息可能慢于写入日志,这样可能出现恢复终点大于on_disk_rba的情况.特别是生产系统出现异常关闭的情况 --//通过例子验证: 1.环境: SYS@book> @ ver1 PORT_STRING VERSION BANNER ------------------------------ -------------- -------------------------------------------------------------------------------- x86_64/Linux 2.4.xx 11.2.0.4.0 Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production 2.测试: --//以sys用户执行: $ cat ac.txt @check.sql create table scott.t tablespace users as select * from all_objects; shutdown abort SYS@book> @ ac.txt 检查点队列当前时间脏块数量 low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT -------------------- -------------------- ---------------- ------------------- --------------------- ---------------- ------------------- ---------------------------- ------------- ------------------- ------------ 822.802.0 822.904.0 13277803650 2020-03-09 09:39:23 822.801.16 13277803347 2020-03-09 09:39:11 303 2 2020-03-09 09:39:26 32 Table created. ORACLE instance shut down. 3.测试: SYS@book> startup mount; ORACLE instance started. Total System Global Area 643084288 bytes Fixed Size 2255872 bytes Variable Size 205521920 bytes Database Buffers 427819008 bytes Redo Buffers 7487488 bytes Database mounted. SYS@book> @ check 检查点队列当前时间脏块数量 low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT -------------------- -------------------- ---------------- ------------------- --------------------- ---------------- ------------------- ---------------------------- ------------- ------------------- ------------ 822.802.0 822.904.0 13277803650 2020-03-09 09:39:23 822.801.16 13277803347 2020-03-09 09:39:11 303 2 2020-03-09 09:40:05 32 --//on_disk_rba=822.904.0.明显不可能，因为我在关闭前建立表t在users表空间里面。 SYS@book> alter database open ; Database altered. SYS@book> @ check 检查点队列当前时间脏块数量 low_rba on_disk_rba on_disk_rba_scn( on_disk_rba_time(CP full checkpoint_rba full_checkpoint( full_checkpoint_tim diff_scn(on_disk_rdb-ch_scn) current_group SYSDATE CPDRT -------------------- -------------------- ---------------- ------------------- --------------------- ---------------- ------------------- ---------------------------- ------------- ------------------- ------------ 823.3.0 823.123.0 13277823928 2020-03-09 09:41:02 823.2.16 13277823734 2020-03-09 09:41:01 194 3 2020-03-09 09:41:05 41 --//检查alert*.log: [2020-03-09 09:41:00] Mon Mar 09 09:41:00 2020 [2020-03-09 09:41:00] alter database open [2020-03-09 09:41:00] Beginning crash recovery of 1 threads [2020-03-09 09:41:01] parallel recovery started with 23 processes [2020-03-09 09:41:01] Started redo scan [2020-03-09 09:41:01] Completed redo scan [2020-03-09 09:41:01] read 10237 KB redo, 90 data blocks need recovery [2020-03-09 09:41:01] Started redo application at [2020-03-09 09:41:01] Thread 1: logseq 822, block 802 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --//等于low_rba=822.802.0.恢复起点。 [2020-03-09 09:41:01] Recovery of Online Redo Log: Thread 1 Group 2 Seq 822 Reading mem 0 [2020-03-09 09:41:01] Mem# 0: /mnt/ramdisk/book/redo02.log [2020-03-09 09:41:01] Completed redo application of 0.12MB [2020-03-09 09:41:01] Completed crash recovery at [2020-03-09 09:41:01] Thread 1: logseq 822, block 21276, scn 13277823731 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [2020-03-09 09:41:01] 90 data blocks read, 90 data blocks written, 10237 redo k-bytes read ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --// 21276-802 = 20474,20474*512/1024 = 10237 K。 --//可以发现恢复到 822.21276.0. 也就是恢复尽可能的读取日志，直到不能读为止。而不是到on_disk_rba=822.904.0结束。 [2020-03-09 09:41:01] Mon Mar 09 09:41:00 2020 [2020-03-09 09:41:01] LGWR: STARTING ARCH PROCESSES [2020-03-09 09:41:01] Mon Mar 09 09:41:00 2020 [2020-03-09 09:41:01] ARC0 started with pid=45, OS id=2352 [2020-03-09 09:41:02] ARC0: Archival started [2020-03-09 09:41:02] LGWR: STARTING ARCH PROCESSES COMPLETE [2020-03-09 09:41:02] ARC0: STARTING ARCH PROCESSES [2020-03-09 09:41:02] Thread 1 advanced to log sequence 823 (thread open) [2020-03-09 09:41:02] Thread 1 opened at log sequence 823 --//切换使用新的日志seq=823，oracle这样做的好处是避免可能的日志覆盖情况。 [2020-03-09 09:41:02] Current log# 3 seq# 823 mem# 0: /mnt/ramdisk/book/redo03.log [2020-03-09 09:41:02] Successful open of redo thread 1 [2020-03-09 09:41:02] MTTR advisory is disabled because FAST_START_MTTR_TARGET is not set [2020-03-09 09:41:02] Mon Mar 09 09:41:01 2020 [2020-03-09 09:41:02] SMON: enabling cache recovery [2020-03-09 09:41:02] Mon Mar 09 09:41:01 2020 [2020-03-09 09:41:02] ARC1 started with pid=46, OS id=2354 [2020-03-09 09:41:02] [2304] Successfully onlined Undo Tablespace 2. [2020-03-09 09:41:02] Undo initialization finished serial:0 start:2332169638 end:2332169688 diff:50 (0 seconds) [2020-03-09 09:41:02] Verifying file header compatibility for 11g tablespace encryption.. [2020-03-09 09:41:02] Verifying 11g file header compatibility for tablespace encryption completed [2020-03-09 09:41:02] SMON: enabling tx recovery [2020-03-09 09:41:02] Database Characterset is ZHS16GBK [2020-03-09 09:41:02] No Resource Manager plan active [2020-03-09 09:41:02] replication_dependency_tracking turned off (no async multimaster replication found) [2020-03-09 09:41:02] WARNING: AQ_TM_PROCESSES is set to 0. System operation might be adversely affected. [2020-03-09 09:41:03] Completed: alter database open [2020-03-09 09:41:03] Mon Mar 09 09:41:02 2020 [2020-03-09 09:41:03] db_recovery_file_dest_size of 61440 MB is 0.00% used. This is a [2020-03-09 09:41:03] user-specified limit on the amount of space that will be used by this [2020-03-09 09:41:03] database for recovery-related files, and does not reflect the amount of [2020-03-09 09:41:03] space available in the underlying filesystem or ASM diskgroup. [2020-03-09 09:41:03] Mon Mar 09 09:41:02 2020 [2020-03-09 09:41:03] Starting background process CJQ0 [2020-03-09 09:41:03] Mon Mar 09 09:41:02 2020 [2020-03-09 09:41:03] CJQ0 started with pid=48, OS id=2370 [2020-03-09 09:41:03] ARC1: Archival started [2020-03-09 09:41:03] ARC0: STARTING ARCH PROCESSES COMPLETE [2020-03-09 09:41:03] ARC0: Becoming the 'no FAL' ARCH [2020-03-09 09:41:03] ARC0: Becoming the 'no SRL' ARCH [2020-03-09 09:41:03] ARC1: Becoming the heartbeat ARCH [2020-03-09 09:41:04] Archived Log entry 1487 added for thread 1 sequence 822 ID 0x4fb7d86e dest 1: [2020-03-09 09:41:04] Mon Mar 09 09:41:03 2020 [2020-03-09 09:41:04] Incremental checkpoint up to RBA [0x337.3.0], current log tail at RBA [0x337.7b.0] --// 0x7b = 123 SYS@book> select count(*) from scott.t; COUNT(*) ------------ 85032 SYS@book> select count(*) from all_objects; COUNT(*) ------------ 85032 --//可以发现建立的表T存在。 4.总结： --//数据库异常关闭恢复的起点是low_rba，终点至少到on_disk_rba,特别在生产系统完成可能超过on_disk_rba，oracle尽量的读取满足需求的日志， --//日志文件里面记录seq号。最后都是切换使用新的日志。 --//大家可以对比http://blog.itpub.net/267265/viewspace-2638170/的测试。 5.脚本check.sql: $ cat check.sql column "full checkpoint_rba" format a21 column low_rba format a20 column low_rba16 format a20 column on_disk_rba format a20 column on_disk_rba16 format a20 column rtckp_rba format a20 column diff_date format 9999999.99 rem column CPOSD_ono_disk_rba_scn format 99999999999999999999999999999999 column cpdrt heading "检查点队列|脏块数量|CPDRT" column cpodt_on_disk_rba heading "检查点队列|on disk rba|时间戳|CPODT" column cpods heading "检查点队列|on disk rba scn|CPODS" column cphbt heading "检查点心跳|CPHBT" column current_sysdate heading "当前时间|SYSDATE" set num 12 SELECT b.cplrba_seq || '.' || b.cplrba_bno || '.' || b.cplrba_bof "low_rba" ,b.cpodr_seq || '.' || b.cpodr_bno || '.' || b.cpodr_bof "on_disk_rba" ,b.CPODS "on_disk_rba_scn(CPODS)" ,TO_DATE (b.CPODT, 'MM-DD-YYYY HH24:MI:SS') "on_disk_rba_time(CPODT)" ,a.rtckp_rba_seq || '.' || a.rtckp_rba_bno || '.' || a.rtckp_rba_bof "full checkpoint_rba" ,a.rtckp_scn "full_checkpoint(rtckp_scn)" ,TO_DATE (a.rtckp_tim, 'MM-DD-YYYY HH24:MI:SS') "full_checkpoint_time_rtckp_tim" ,b.CPODS - a.rtckp_scn "diff_scn(on_disk_rdb-ch_scn)" ,a.rtcln "current_group" ,sysdate current_sysdate ,CPDRT FROM x$kccrt a, x$kcccp b WHERE a.rtnum = b.cptno AND A.INST_ID = b.inst_id;

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