了解你所不知道的SMON功能(六):Instance Recovery

SMON的作用还包括RAC环境中的Instance Recovery,注意虽然Instance Recovery可以翻做实例恢复,但实际上和我们口头所说的实例恢复是不同的。我们口头语言所说的实例恢复很大程度上是指Crash Recovery崩溃恢复,Instance Recovery与Crash Recovery是存在区别的:针对单实例(single instance)或者RAC中所有节点全部崩溃后的恢复,我们称之为Crash Recovery。而对于RAC中的某一个节点失败,存活节点(surviving instance)试图对失败节点线程上redo做应用的情况,我们称之为Instance Recovery。对于Crash Recovery更多的内容可见<还原真实的cache recovery>一文。

现象

Instance Recovery期间分别存在cache recovery和ges/gcs remaster2个recovery stage,注意这2个舞台的恢复是同时进行的。cache recovery的主角是存活节点上的SMON进程,SMON负责分发redo给slave进程。而实施ges/gcs remaster的是RAC专有进程LMON。

整个Reconfiuration的过程如下图:
rac_instance_recovery_reconfiguration
 
注意以上Crash Detected时数据库进入部分可用(Partial Availability)状态,从Freeze Lockdb开始None Availability,到IR applies redo即前滚时转换为Partial Availability,待前滚完成后会实施回滚,但是此时数据库已经进入完全可用(Full Availability)状态了,如下图:
 
oracledatabase12g_instance_recovery

The graphic illustrates the degree of database availability during each step of Oracle instance recovery: 

A.         Real Application Clusters is running on multiple nodes.

B.         Node failure is detected.

C.         The enqueue part of the GRD is reconfigured; resource management is redistributed to the surviving nodes. This operation occurs relatively quickly.

D.        The cache part of the GRD is reconfigured and SMON reads the redo log of the failed instance to identify the database blocks that it needs to recover.

E.         SMON issues the GRD requests to obtain all the database blocks it needs for recovery. After the requests are complete, all other blocks are accessible.

F.         The Oracle server performs roll forward recovery. Redo logs of the failed threads are applied to the database, and blocks are available right after their recovery is completed.

G.        The Oracle server performs rollback recovery. Undo blocks are applied to the database for all uncommitted transactions.

H.        Instance recovery is complete and all data is accessible.

Note: The dashed line represents the blocks identified in step 2 in the previous slide. Also, the dotted steps represent the ones identified in the previous slide.

我们来实际观察一下Instance Recovery的过程:

INST 1:
SQL> select * from v$version;
BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE    11.2.0.2.0      Production
TNS for Linux: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production
SQL> select * from global_name;
GLOBAL_NAME
--------------------------------------------------------------------------------
www.askmaclean.com
SQL> alter system set event='10426 trace name context forever,level 12' scope=spfile;  -- 10426 event Reconfiguration trace event
System altered.
SQL> startup force;
ORACLE instance started.
INST 2:
SQL> shutdown abort
ORACLE instance shut down.

=============================================================
========================alert.log============================
Reconfiguration started (old inc 4, new inc 6)
List of instances:
1 (myinst: 1)
 Global Resource Directory frozen
* dead instance detected - domain 0 invalid = TRUE
Communication channels reestablished
Master broadcasted resource hash value bitmaps
Non-local Process blocks cleaned out
LMS 0: 0 GCS shadows cancelled, 0 closed, 0 Xw survived
Set master node info
Submitted all remote-enqueue requests
Dwn-cvts replayed, VALBLKs dubious
All grantable enqueues granted
 Post SMON to start 1st pass IR
Instance recovery: looking for dead threads
Beginning instance recovery of 1 threads
parallel recovery started with 2 processes                 --2 recovery slave
Submitted all GCS remote-cache requests
Post SMON to start 1st pass IR
Fix write in gcs resources
Reconfiguration complete
Started redo scan
Completed redo scan
read 88 KB redo, 82 data blocks need recovery
Started redo application at
Thread 2: logseq 374, block 2, scn 54624376
Recovery of Online Redo Log: Thread 2 Group 4 Seq 374 Reading mem 0
Mem# 0: +DATA/prod/onlinelog/group_4.271.747100549
Mem# 1: +DATA/prod/onlinelog/group_4.272.747100553
Completed redo application of 0.07MB
Completed instance recovery at
Thread 2: logseq 374, block 178, scn 54646382
73 data blocks read, 83 data blocks written, 88 redo k-bytes read
Thread 2 advanced to log sequence 375 (thread recovery)
Redo thread 2 internally disabled at seq 375 (SMON)
ARC3: Creating local archive destination LOG_ARCHIVE_DEST_1: '/s01/arch/2_374_747100216.dbf' (thread 2 sequence 374) (PROD1)
Setting Resource Manager plan SCHEDULER[0x310B]:DEFAULT_MAINTENANCE_PLAN via scheduler window
Setting Resource Manager plan DEFAULT_MAINTENANCE_PLAN via parameter
ARC3: Closing local archive destination LOG_ARCHIVE_DEST_1: '/s01/arch/2_374_747100216.dbf' (PROD1)
2011-06-27 22:19:29.280000 +08:00
Archived Log entry 792 added for thread 2 sequence 374 ID 0x9790ab2 dest 1:
ARC0: Creating local archive destination LOG_ARCHIVE_DEST_1: '/s01/arch/2_375_747100216.dbf' (thread 2 sequence 375) (PROD1)
2011-06-27 22:19:30.336000 +08:00
ARC0: Archiving disabled thread 2 sequence 375
ARC0: Closing local archive destination LOG_ARCHIVE_DEST_1: '/s01/arch/2_375_747100216.dbf' (PROD1)
Archived Log entry 793 added for thread 2 sequence 375 ID 0x9790ab2 dest 1:
minact-scn: Master considers inst:2 dead

==================================================================
===========================smon trace begin=======================

*** 2011-06-27 22:19:28.279
2011-06-27 22:19:28.279849 : Start recovery for domain=0, valid=0, flags=0x0
Successfully allocated 2 recovery slaves
Using 67 overflow buffers per recovery slave
Thread 2 checkpoint: logseq 374, block 2, scn 54624376
cache-low rba: logseq 374, block 2
on-disk rba: logseq 374, block 178, scn 54626382
start recovery at logseq 374, block 2, scn 54624376
Instance recovery not required for thread 1
*** 2011-06-27 22:19:28.487
Started writing zeroblks thread 2 seq 374 blocks 178-185
*** 2011-06-27 22:19:28.487
Completed writing zeroblks thread 2 seq 374
==== Redo read statistics for thread 2 ====
Total physical reads (from disk and memory): 4096Kb
-- Redo read_disk statistics --
Read rate (ASYNC): 88Kb in 0.18s => 0.48 Mb/sec
Longest record: 8Kb, moves: 0/186 (0%)
Longest LWN: 33Kb, moves: 0/47 (0%), moved: 0Mb
Last redo scn: 0x0000.0341884d (54626381)
----------------------------------------------
----- Recovery Hash Table Statistics ---------
Hash table buckets = 262144
Longest hash chain = 1
Average hash chain = 82/82 = 1.0
Max compares per lookup = 1
Avg compares per lookup = 248/330 = 0.8
----------------------------------------------
*** 2011-06-27 22:19:28.489
KCRA: start recovery claims for 82 data blocks
*** 2011-06-27 22:19:28.526
KCRA: blocks processed = 82/82, claimed = 81, eliminated = 1
2011-06-27 22:19:28.526088 : Validate domain 0
**************** BEGIN RECOVERY HA STATS  ****************

I'm the recovery instance
smon posted (1278500359646), recovery started 0.027 secs,(1278500359673)
domain validated 0.242 secs (1278500359888)
claims opened 70, claims converted 11, claims preread 0
****************  END RECOVERY HA STATS  *****************
2011-06-27 22:19:28.526668 : Validated domain 0, flags = 0x0
*** 2011-06-27 22:19:28.556
Recovery of Online Redo Log: Thread 2 Group 4 Seq 374 Reading mem 0
*** 2011-06-27 22:19:28.560
Completed redo application of 0.07MB
*** 2011-06-27 22:19:28.569
Completed recovery checkpoint
----- Recovery Hash Table Statistics ---------
Hash table buckets = 262144
Longest hash chain = 1
Average hash chain = 82/82 = 1.0
Max compares per lookup = 1
Avg compares per lookup = 330/330 = 1.0
----------------------------------------------
*** 2011-06-27 22:19:28.572 5401 krsg.c
Acquiring RECOVERY INFO PING latch from [krsg.c:5401] IX0
*** 2011-06-27 22:19:28.572 5401 krsg.c
Successfully acquired RECOVERY INFO PING latch IX+
*** 2011-06-27 22:19:28.572 5406 krsg.c
Freeing RECOVERY INFO PING latch from [krsg.c:5406] IX0
*** 2011-06-27 22:19:28.572 5406 krsg.c
Successfully freed RECOVERY INFO PING latch IX-
krss_sched_work: Prod archiver request from process SMON (function:0x2000)
krss_find_arc: Evaluating ARC3 to receive message (flags 0x0)
krss_find_arc: Evaluating ARC0 to receive message (flags 0x0)
krss_find_arc: Evaluating ARC1 to receive message (flags 0xc)
krss_find_arc: Evaluating ARC2 to receive message (flags 0x2)
krss_find_arc: Selecting ARC2 to receive REC PING message
*** 2011-06-27 22:19:28.572 3093 krsv.c
krsv_send_msg: Sending message to process ARC2
*** 2011-06-27 22:19:28.572 1819 krss.c
krss_send_arc: Sent message to ARC2 (message:0x2000)
Recovery sets nab of thread 2 seq 374 to 178 with 8 zeroblks
Retrieving log 4
pre-aal: xlno:4 flno:0 arf:0 arb:2 arh:2 art:4
Updating log 3 thread 2 sequence 375
Previous log 3 thread 2 sequence 0
Updating log 4 thread 2 sequence 374
Previous log 4 thread 2 sequence 374
post-aal: xlno:4 flno:0 arf:3 arb:2 arh:2 art:3
krss_sched_work: Prod archiver request from process SMON (function:0x1)
krss_find_arc: Evaluating ARC3 to receive message (flags 0x0)
krss_find_arc: Selecting ARC3 to receive message
*** 2011-06-27 22:19:28.589 3093 krsv.c
krsv_send_msg: Sending message to process ARC3
*** 2011-06-27 22:19:28.589 1819 krss.c
krss_send_arc: Sent message to ARC3 (message:0x1)
Retrieving log 2
Kicking thread 1 to switch logfile
Retrieving log 4
Retrieving log 3
krss_sched_work: Prod archiver request from process SMON (function:0x1)
krss_find_arc: Evaluating ARC0 to receive message (flags 0x0)
krss_find_arc: Selecting ARC0 to receive message
*** 2011-06-27 22:19:28.599 3093 krsv.c
krsv_send_msg: Sending message to process ARC0
*** 2011-06-27 22:19:28.599 1819 krss.c
krss_send_arc: Sent message to ARC0 (message:0x1)
*** 2011-06-27 22:19:28.599 838 krsv.c
krsv_dpga: Waiting for pending I/O to complete
*** 2011-06-27 22:19:29.304
krss_sched_work: Prod archiver request from process SMON (function:0x1)
krss_find_arc: Evaluating ARC1 to receive message (flags 0xc)
krss_find_arc: Selecting ARC1 to receive message
*** 2011-06-27 22:19:29.304 3093 krsv.c
krsv_send_msg: Sending message to process ARC1
*** 2011-06-27 22:19:29.304 1819 krss.c
krss_send_arc: Sent message to ARC1 (message:0x1)
SMON[INST-TXN-RECO]:about to recover undo segment 11 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 11 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 12 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 12 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 13 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 13 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 14 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 14 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 15 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 15 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 16 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 16 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 17 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 17 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 18 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 18 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 19 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 19 as available status:2 ret:0
SMON[INST-TXN-RECO]:about to recover undo segment 20 status:3 inst:2
SMON[INST-TXN-RECO]: mark undo segment 20 as available status:2 ret:0
*** 2011-06-27 22:19:43.299
* kju_tsn_aff_drm_pending TRACEUD: called with tsn x2, dissolve 0
* kju_tsn_aff_drm_pending TRACEUD: tsn_pkey = x2.1
* >> RM REQ QS ---:
single window RM request queue is empty
multi-window RM request queue is empty
* Global DRM state ---:
There is no dynamic remastering
RM lock state = 0
pkey 2.1 undo 1 stat 0 masters[32768, 1->1] reminc 4 RM# 1
flg x0 type x0 afftime x36e6e3a8
nreplays by lms 0 = 0
* kju_tsn_aff_drm_pending TRACEUD: matching request not found on swin queue
* kju_tsn_aff_drm_pending TRACEUD: pp found, stat x0
* kju_tsn_aff_drm_pending TRACEUD: 2 return true
*** 2011-06-27 22:22:18.333
* kju_tsn_aff_drm_pending TRACEUD: called with tsn x2, dissolve 0
* kju_tsn_aff_drm_pending TRACEUD: tsn_pkey = x2.1
* >> RM REQ QS ---:
single window RM request queue is empty
multi-window RM request queue is empty
* Global DRM state ---:
There is no dynamic remastering
RM lock state = 0
pkey 2.1 undo 1 stat 0 masters[32768, 1->1] reminc 4 RM# 1
flg x0 type x0 afftime x36e6e3a8
nreplays by lms 0 = 0
* kju_tsn_aff_drm_pending TRACEUD: matching request not found on swin queue
* kju_tsn_aff_drm_pending TRACEUD: pp found, stat x0
* kju_tsn_aff_drm_pending TRACEUD: 2 return true
*** 2011-06-27 22:24:53.365
* kju_tsn_aff_drm_pending TRACEUD: called with tsn x2, dissolve 0
* kju_tsn_aff_drm_pending TRACEUD: tsn_pkey = x2.1
* >> RM REQ QS ---:
single window RM request queue is empty
multi-window RM request queue is empty
* Global DRM state ---:
There is no dynamic remastering
RM lock state = 0
pkey 2.1 undo 1 stat 0 masters[32768, 1->1] reminc 4 RM# 1
flg x0 type x0 afftime x36e6e3a8
nreplays by lms 0 = 0
* kju_tsn_aff_drm_pending TRACEUD: matching request not found on swin queue
* kju_tsn_aff_drm_pending TRACEUD: pp found, stat x0
* kju_tsn_aff_drm_pending TRACEUD: 2 return true
========================================================================
==============================lmon trace begin==========================
 *** 2011-06-27 22:19:27.748
kjxgmpoll reconfig instance map: 1
*** 2011-06-27 22:19:27.748
kjxgmrcfg: Reconfiguration started, type 1
CGS/IMR TIMEOUTS:
CSS recovery timeout = 31 sec (Total CSS waittime = 65)
IMR Reconfig timeout = 75 sec
CGS rcfg timeout = 85 sec
kjxgmcs: Setting state to 4 0.
*** 2011-06-27 22:19:27.759
Name Service frozen
kjxgmcs: Setting state to 4 1.
kjxgrdecidever: No old version members in the cluster
kjxgrssvote: reconfig bitmap chksum 0x2137452d cnt 1 master 1 ret 0
kjxgrpropmsg: SSMEMI: inst 1 - no disk vote
kjxgrpropmsg: SSVOTE: Master indicates no Disk Voting
2011-06-27 22:19:27.760783 : kjxgrDiskVote: nonblocking method is chosen
kjxggpoll: change poll time to 50 ms
2011-06-27 22:19:27.918847 : kjxgrDiskVote: Obtained RR update lock for sequence 5, RR seq 4
2011-06-27 22:19:28.023160 : kjxgrDiskVote: derive membership from CSS (no disk votes)
2011-06-27 22:19:28.023240 : proposed membership: 1
*** 2011-06-27 22:19:28.081
2011-06-27 22:19:28.081952 : kjxgrDiskVote: new membership is updated by inst 1, seq 6
2011-06-27 22:19:28.082073 : kjxgrDiskVote: bitmap: 1
CGS/IMR TIMEOUTS:
CSS recovery timeout = 31 sec (Total CSS waittime = 65)
IMR Reconfig timeout = 75 sec
CGS rcfg timeout = 85 sec
kjxgmmeminfo: can not invalidate inst 2
kjxgmps: proposing substate 2
kjxgmcs: Setting state to 6 2.
kjfmSendAbortInstMsg: send an abort message to instance 2
kjfmuin: inst bitmap 1
kjfmmhi: received msg from inst 1 (inc 2)
Performed the unique instance identification check
kjxgmps: proposing substate 3
kjxgmcs: Setting state to 6 3.
Name Service recovery started
Deleted all dead-instance name entries
kjxgmps: proposing substate 4
kjxgmcs: Setting state to 6 4.
Multicasted all local name entries for publish
Replayed all pending requests
kjxgmps: proposing substate 5
kjxgmcs: Setting state to 6 5.
Name Service normal
Name Service recovery done
*** 2011-06-27 22:19:28.191
kjxgmps: proposing substate 6
kjxgmcs: Setting state to 6 6.
kjxgmcs: total reconfig time 0.432 seconds (from 2895072218 to 2895072650)
kjxggpoll: change poll time to 600 ms
kjfmact: call ksimdic on instance (2)
2011-06-27 22:19:28.211846 :
********* kjfcrfg() called, BEGIN LMON RCFG *********
2011-06-27 22:19:28.211906 : * Begin lmon rcfg step KJGA_RCFG_BEGIN
* kjfcrfg: Resource broadcasting disabled
* kjfcrfg: kjfcqiora returned success
kjfcrfg: DRM window size = 4096->4096 (min lognb = 15)
2011-06-27 22:19:28.211954 :
Reconfiguration started (old inc 4, new inc 6)
TIMEOUTS:
Local health check timeout: 70 sec
Rcfg process freeze timeout: 70 sec
Remote health check timeout: 140 sec
Defer Queue timeout: 163 secs
CGS rcfg timeout: 85 sec
Synchronization timeout: 248 sec
DLM rcfg timeout: 744 sec
List of instances:
1 (myinst: 1)
Undo tsn affinity 1
OMF 0
2011-06-27 22:19:28.212394 : * Begin lmon rcfg step KJGA_RCFG_FREEZE

*** 2011-06-27 22:19:28.233
* published: inc 6, isnested 0, rora req 0,
rora start 0, rora invalid 0, (roram 32767), isrcvinst 1,
(rcvinst 1), isdbopen 1, drh 0, (myinst 1)
thread 1, isdbmounted 1, sid hash x0
* kjfcrfg: published bigns successfully
* Force-published at step 3
2011-06-27 22:19:28.233575 :  Global Resource Directory frozen
* roram 32767, rcvinst 1
* kjfc_thread_qry: instance 1 flag 3 thread 1 sid 0
* kjfcrfg: queried bigns successfully
inst 1
* kjfcrfg: single_instance_kjga = TRUE
asby init, 0/1/x2
asby returns, 0/1/x2/false
* Domain maps before reconfiguration:
*   DOMAIN 0 (valid 1): 1 2
* End of domain mappings
* dead instance detected - domain 0 invalid = TRUE
* Domain maps after recomputation:
*   DOMAIN 0 (valid 0): 1
* End of domain mappings
2011-06-27 22:19:28.235110 : * Begin lmon rcfg step KJGA_RCFG_COMM
2011-06-27 22:19:28.235242 : GSIPC:KSXPCB: msg 0xd8b84550 status 34, type 2, dest 2, rcvr 0
2011-06-27 22:19:28.235339 : GSIPC:KSXPCB: msg 0xd8b80180 status 34, type 2, dest 2, rcvr 1
Active Sendback Threshold = 50 %
Communication channels reestablished
2011-06-27 22:19:28.240076 : * Begin lmon rcfg step KJGA_RCFG_EXCHANGE
2011-06-27 22:19:28.240192 : * Begin lmon rcfg step KJGA_RCFG_ENQCLEANUP
Master broadcasted resource hash value bitmaps
2011-06-27 22:19:28.251474 :
Non-local Process blocks cleaned out
2011-06-27 22:19:28.251822 : * Begin lmon rcfg step KJGA_RCFG_CLEANUP
2011-06-27 22:19:28.265220 : * Begin lmon rcfg step KJGA_RCFG_TIMERQ
2011-06-27 22:19:28.265308 : * Begin lmon rcfg step KJGA_RCFG_DDQ
2011-06-27 22:19:28.265393 : * Begin lmon rcfg step KJGA_RCFG_SETMASTER
2011-06-27 22:19:28.271551 :
Set master node info
2011-06-27 22:19:28.271931 : * Begin lmon rcfg step KJGA_RCFG_ENQREPLAY
2011-06-27 22:19:28.275490 :  Submitted all remote-enqueue requests
2011-06-27 22:19:28.275596 : * Begin lmon rcfg step KJGA_RCFG_ENQDUBIOUS
Dwn-cvts replayed, VALBLKs dubious
2011-06-27 22:19:28.277223 : * Begin lmon rcfg step KJGA_RCFG_ENQGRANT
All grantable enqueues granted
2011-06-27 22:19:28.277992 : * Begin lmon rcfg step KJGA_RCFG_PCMREPLAY
2011-06-27 22:19:28.279234 :
2011-06-27 22:19:28.279255 :  Post SMON to start 1st pass IR               --SMON posted by LMON
2011-06-27 22:19:28.307890 :  Submitted all GCS cache requests             --IR acquires all gcs resource needed for recovery
2011-06-27 22:19:28.308038 : * Begin lmon rcfg step KJGA_RCFG_FIXWRITES
Post SMON to start 1st pass IR
Fix write in gcs resources
2011-06-27 22:19:28.313508 : * Begin lmon rcfg step KJGA_RCFG_END
2011-06-27 22:19:28.313720 :
2011-06-27 22:19:28.313733 :
Reconfiguration complete
*   domain 0 valid?: 0
* kjfcrfg: ask RMS0 to do pnp work
**************** BEGIN DLM RCFG HA STATS  ****************
Total dlm rcfg time (inc 6): 0.100 secs (1278500359581, 1278500359681)
Begin step .........: 0.001 secs (1278500359581, 1278500359582)
Freeze step ........: 0.020 secs (1278500359582, 1278500359602)
Remap step .........: 0.002 secs (1278500359602, 1278500359604)
Comm step ..........: 0.005 secs (1278500359604, 1278500359609)
Sync 1 step ........: 0.000 secs (0, 0)
Exchange step ......: 0.000 secs (1278500359609, 1278500359609)
Sync 2 step ........: 0.000 secs (0, 0)
Enqueue cleanup step: 0.011 secs (1278500359609, 1278500359620)
Sync pcm1 step .....: 0.000 secs (0, 0)
Cleanup step .......: 0.013 secs (1278500359620, 1278500359633)
Timerq step ........: 0.000 secs (1278500359633, 1278500359633)
Ddq step ...........: 0.000 secs (1278500359633, 1278500359633)
Set master step ....: 0.006 secs (1278500359633, 1278500359639)
Sync 3 step ........: 0.000 secs (0, 0)
Enqueue replay step : 0.004 secs (1278500359639, 1278500359643)
Sync 4 step ........: 0.000 secs (0, 0)
Enqueue dubious step: 0.001 secs (1278500359643, 1278500359644)
Sync 5 step ........: 0.000 secs (0, 0)
Enqueue grant step .: 0.001 secs (1278500359644, 1278500359645)
Sync 6 step ........: 0.000 secs (0, 0)
PCM replay step ....: 0.030 secs (1278500359645, 1278500359675)
Sync 7 step ........: 0.000 secs (0, 0)
Fixwrt replay step .: 0.003 secs (1278500359675, 1278500359678)
Sync 8 step ........: 0.000 secs (0, 0)
End step ...........: 0.001 secs (1278500359680, 1278500359681)
Number of replayed enqueues sent / received .......: 0 / 0
Number of replayed fusion locks sent / received ...: 0 / 0
Number of enqueues mastered before / after rcfg ...: 2217 / 2941
Number of fusion locks mastered before / after rcfg: 3120 / 5747
****************  END DLM RCFG HA STATS  *****************
*** 2011-06-27 22:19:36.589
kjxgfipccb: msg 0x0x7ff526139320, mbo 0x0x7ff526139310, type 19, ack 0, ref 0, stat 34
=====================================================================
============================lms trace begin==========================

*** 2011-06-27 22:38:54.663
2011-06-27 22:38:54.663764 :  0 GCS shadows cancelled, 0 closed, 0 Xw survived
2011-06-27 22:38:54.673539 :  5230 GCS resources traversed, 0 cancelled
2011-06-27 22:38:54.707671 :  9322 GCS shadows traversed, 0 replayed, 0 duplicates,
5183 not replayed, dissolve 0 timeout 0 RCFG(10) lms 0 finished replaying gcs resources
2011-06-27 22:38:54.709132 :  0 write requests issued in 384 GCS resources        --check past image
 0 PIs marked suspect, 0 flush PI msgs
2011-06-27 22:38:54.709520 :  0 write requests issued in 273 GCS resources
1 PIs marked suspect, 0 flush PI msgs
2011-06-27 22:38:54.709842 :  0 write requests issued in 281 GCS resources
0 PIs marked suspect, 0 flush PI msgs
2011-06-27 22:38:54.710159 :  0 write requests issued in 233 GCS resources
0 PIs marked suspect, 0 flush PI msgs
2011-06-27 22:38:54.710531 :  0 write requests issued in 350 GCS resources
lms 0 finished fixing gcs write protocol

Instance Recovery和普通的Crash Recovery最大的区别在于实例恢复过程中的GRD Frozen和对GES/GCS资源的Remaster,这部分工作主要由LMON进程完成,可以从以上trace中发现一些KJGA_RCFG_*形式的Reconfiguration步骤,它们的含义:

Reconfiguration Steps:
1.    KJGA_RCFG_BEGIN
LMON continuously polling for reconfiguration event. Once cgs reports a change in cluster membership,
LMON starts reconfiguration
2.    KJGA_RCFG_FREEZE
All processes acknowledges to the reconfiguration freeze before LMON continue 
3.    KJGA_RCFG_REMAP
Updates new instance map (kjfchsu), re-distributes resource mastership. Invalidate recovery domains
if reconfiguration is caused by instance death.
4.    KJGA_RCFG_COMM
Reinitialize communication channel
5.    KJGA_RCFG_EXCHANGE
Exchange of master information of gcs, ges and file affinity master
6.    KJGA_RCFG_ENQCLEANUP
Delete remote dead gcs/ges locks. Cancel converting gcs requests. 
7.    KJGA_RCFG_CLEANUP
Cleanup/remove ges resources
8.    KJGA_RCFG_TIMERQ
Restore relative timeout for enqueue locks on timeout queue
9.    KJGA_RCFG_DDQ
Clean out enqueue locks on deadlock queue
10.  KJGA_RCFG_SETMASTER
Update master info for each enqueue resources that need to be remastered.
11.  KJGA_RCFG_REPLAY
Replay enqueue locks
12.  KJGA_RCFG_ENQDUBIOUS
Invalidates ges resources without established value
13.  KJGA_RCFG_ENQGRANT
Grants all grantable ges lock requests
14.  KJGA_RCFG_REPLAY2
Enqueue reconfiguration complete. Post SMON to start instance recovery.  Starts replaying gcs resources.
15.  KJGA_RCFG_FIXWRITES2
Fix write state of gcs resources
16.  KJGA_RCFG_END
Unfreeze lock database

Instance Recovery相关的诊断事件
我们无法禁止Instance Recovery的发生,事实上一旦出现Instance Crash那么Instance Recovery就是必须的。
与Instance Recovery相关的诊断事件主要有10426和29717等:

    10426 – Reconfiguration trace event
10425 – Enqueue operations
10432 – Fusion activity
10429 – IPC tracing
oerr ora 10425
10425, 00000, "enable global enqueue operations event trace"
// *Document: NO
// *Cause:
// *Action: Dump trace for global enqueue operations.
oerr ora 10426
10426, 00000, "enable ges/gcs reconfiguration event trace"
// *Document: NO
// *Cause:
// *Action: Dump trace for ges/gcs reconfiguration.
oerr ora 10430
10430, 00000, "enable ges/gcs dynamic remastering event trace"
// *Document: NO
// *Cause:
// *Action: Dump trace for ges/gcs dynamic remastering.
oerr ora 10401
10401, 00000, "turn on IPC (ksxp) debugging"
// *Cause:
// *Action: Enables debugging code for IPC service layer (ksxp)
oerr ora 10708
10708, 00000, "print out trace information from the RAC buffer cache"
// *Cause: N/A
// *Action: THIS IS NOT A USER ERROR NUMBER/MESSAGE.  THIS DOES NOT NEED TO BE
//          TRANSLATED OR DOCUMENTED. IT IS USED ONLY FOR DEBUGGING.
oerr ora 29717
29717, 00000, "enable global resource directory freeze/unfreeze event trace"
// *Document: NO
// *Cause:
// *Action: Dump trace for global resource directory freeze/unfreeze.
diag RAC INSTANCE SHUTDOWN LMON
LMON will dump more informations to trace during reconfig and freeze.
event="10426 trace name context forever, level 8"
event="29717 trace name context forever, level 5"
or
event="10426 trace name context forever, level 12"
event="10430 trace name context forever, level 12"
event="10401 trace name context forever, level 8"
event="10046 trace name context forever, level 8"
event="10708 trace name context forever, level 15"
event="29717 trace name context forever, level 5"
see 29717  grd frozen trace

alter system set event='29717 trace name context forever, level 5' scope=spfile;
=========================================================================
============================lmon trace begin=============================
********* kjfcrfg() called, BEGIN LMON RCFG *********
2011-06-27 23:13:16.693089 : * Begin lmon rcfg step KJGA_RCFG_BEGIN
* kjfcrfg: Resource broadcasting disabled
* kjfcrfg: kjfcqiora returned success
kjfcrfg: DRM window size = 4096->4096 (min lognb = 15)
2011-06-27 23:13:16.693219 :
Reconfiguration started (old inc 4, new inc 6)
TIMEOUTS:
Local health check timeout: 70 sec
Rcfg process freeze timeout: 70 sec
Remote health check timeout: 140 sec
Defer Queue timeout: 163 secs
CGS rcfg timeout: 85 sec
Synchronization timeout: 248 sec
DLM rcfg timeout: 744 sec
List of instances:
1 (myinst: 1)
Undo tsn affinity 1
OMF 0
[FDB][start]
2011-06-27 23:13:16.701320 : * Begin lmon rcfg step KJGA_RCFG_FREEZE
[FACK][18711 not frozen]          --fack means acknowledge in advance
[FACK][18713 not frozen]
[FACK][18719 not frozen]
[FACK][18721 not frozen]
[FACK][18723 not frozen]
[FACK][18729 not frozen]
[FACK][18739 not frozen]
[FACK][18743 not frozen]
[FACK][18745 not frozen]
[FACK][18747 not frozen]
[FACK][18749 not frozen]
[FACK][18751 not frozen]
[FACK][18753 not frozen]
[FACK][18755 not frozen]
[FACK][18757 not frozen]
[FACK][18759 not frozen]
[FACK][18763 not frozen]
[FACK][18765 not frozen]
[FACK][18767 not frozen]
[FACK][18769 not frozen]
[FACK][18771 not frozen]
[FACK][18775 not frozen]
[FACK][18777 not frozen]
[FACK][18816 not frozen]
[FACK][18812 not frozen]
[FACK][18818 not frozen]
[FACK][18820 not frozen]
[FACK][18824 not frozen]
[FACK][18826 not frozen]
[FACK][18830 not frozen]
[FACK][18835 not frozen]
[FACK][18842 not frozen]
[FACK][18860 not frozen]
[FACK][18865 not frozen]
[FACK][18881 not frozen]
[FACK][18883 not frozen]
[FACK][18909 not frozen]
*** 2011-06-27 23:13:16.724
* published: inc 6, isnested 0, rora req 0,
rora start 0, rora invalid 0, (roram 32767), isrcvinst 0,
(rcvinst 32767), isdbopen 1, drh 0, (myinst 1)
thread 1, isdbmounted 1, sid hash x0
* kjfcrfg: published bigns successfully
* Force-published at step 3
2011-06-27 23:13:16.724764 :  Global Resource Directory frozen
* kjfc_qry_bigns: noone has the rcvinst established yet, set it to the highest open instance = 1
* roram 32767, rcvinst 1
* kjfc_thread_qry: instance 1 flag 3 thread 1 sid 0
* kjfcrfg: queried bigns successfully

=====================================================================
==========================lmd0 trace begin===========================
*** 2011-06-27 23:13:16.700
[FFCLI][frozen]
[FUFCLI][normal]

还原真实的cache recovery

我们在学习Oracle基础知识的时候会了解到实例恢复(Instance Recovery)或者说崩溃恢复(Crash recovery)的概念,有时候甚至于这2个名词在我们日常的语言中表达同样的意思。实际上Instance Recovery与Crash Recovery是存在区别的:针对单实例(single instance)或者RAC中所有节点全部崩溃后的恢复,我们称之为Crash Recovery。而对于RAC中的某一个节点失败,存活节点(surviving instance)试图对失败节点线程上redo做应用的情况,我们称之为Instance Recovery。

不管是Instance Recovery还是Crash Recovery,都由2个部分组成:cache recovery继以transaction recovery。

根据官方文档的介绍,Cache Recovery也叫Rolling Forward,就是我们常说的前滚;而Transaction Recovery也叫Rolling Back,就是我们常说的回滚。前滚和回滚贯穿Oracle恢复的基本概念,是我们入门必要学习的知识,在次不多介绍。

有文事者,必济之以武略。理论学得再好,不实践也无用。所幸Crash Recovery是很容易做成的实验,我们不妨来看一看:

SQL> shutdown abort;
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 1065353216 bytes
Fixed Size                  2089336 bytes
Variable Size             486542984 bytes
Database Buffers          570425344 bytes
Redo Buffers                6295552 bytes
Database mounted.
SQL> alter database open;
Crash Recovery将从alter database open开始,我们来观察其日志
==================alert.log====================
alter database open
Tue Jun 14 18:19:53 2011
Beginning crash recovery of 1 threads
parallel recovery started with 2 processes
Tue Jun 14 18:19:53 2011
Started redo scan
Tue Jun 14 18:19:53 2011
Completed redo scan
0 redo blocks read, 0 data blocks need recovery
Tue Jun 14 18:19:53 2011
Started redo application at
Thread 1: logseq 1004, block 1124, scn 17136185
Tue Jun 14 18:19:53 2011
Recovery of Online Redo Log: Thread 1 Group 2 Seq 1004 Reading mem 0
Mem# 0: /flashcard/oradata/G10R2/onlinelog/o1_mf_2_6v34jokt_.log
Mem# 1: /s01/flash_recovery_area/G10R2/onlinelog/o1_mf_2_6v34jotq_.log
Tue Jun 14 18:19:53 2011
Completed redo application
Tue Jun 14 18:19:53 2011
Completed crash recovery at
Thread 1: logseq 1004, block 1124, scn 17156186
0 data blocks read, 0 data blocks written, 0 redo blocks read
Tue Jun 14 18:19:53 2011
LGWR: STARTING ARCH PROCESSES
ARC0: Archival started
LGWR: STARTING ARCH PROCESSES COMPLETE
ARC0 started with pid=16, OS id=7829
Tue Jun 14 18:19:53 2011
Thread 1 advanced to log sequence 1005 (thread open)
Thread 1 opened at log sequence 1005
Current log# 3 seq# 1005 mem# 0: /flashcard/oradata/G10R2/onlinelog/o1_mf_3_6v34jpmp_.log
Current log# 3 seq# 1005 mem# 1: /s01/flash_recovery_area/G10R2/onlinelog/o1_mf_3_6v34jpyn_.log
Successful open of redo thread 1
Tue Jun 14 18:19:53 2011
ARC0: Becoming the 'no FAL' ARCH
ARC0: Becoming the 'no SRL' ARCH
ARC0: Becoming the heartbeat ARCH
Tue Jun 14 18:19:53 2011
SMON: enabling cache recovery
Tue Jun 14 18:19:53 2011
db_recovery_file_dest_size of 204800 MB is 6.81% used. This is a
user-specified limit on the amount of space that will be used by this
database for recovery-related files, and does not reflect the amount of
space available in the underlying filesystem or ASM diskgroup.
Tue Jun 14 18:19:54 2011
Successfully onlined Undo Tablespace 1.
Tue Jun 14 18:19:54 2011
SMON: enabling tx recovery
Database Characterset is UTF8
Opening with internal Resource Manager plan
where NUMA PG = 1, CPUs = 2
replication_dependency_tracking turned off (no async multimaster replication found)
Starting background process QMNC
QMNC started with pid=17, OS id=7831
Tue Jun 14 18:19:55 2011
Completed: alter database open

注意上述单实例Crash Recovery到数据库打开的整个过程:

  • alter database open
  • Beginning crash recovery of 1 threads
  • Started redo scan
  • Completed redo scan
  • Started redo application at
  • Completed redo application
  • Completed crash recovery at
  • SMON: enabling cache recovery
  • Successfully onlined Undo Tablespace 1
  • SMON: enabling tx recovery
  • Completed: alter database open

从上述步骤中我们可以看到三种恢复名词,即:

  • crash recovery
  • cache recovery
  • tx recovery

这和官方文档所描述的Crash Recovery概念是不一致的,我们现在来理清这几种recovery。

crash recovery包含对redo的scan和application,显然其完成的是Rolling Forward前滚的工作,告警日志中出现的crash recovery等同于官方文档中介绍的”cache recovery”,我们可以将” Completed crash recovery”看做前滚完成的标志。而tx recovery从字面就可以看出实际上是Transaction Recovery,tx recovery发生在Undo Tablespace online之后(回滚事务的前提是Undo可用),数据完成打开操作之前(“Completed: alter database open”)。注意tx recovery并不要求数据库打开前完成,仅仅是在数据库打开之前由smon启动(“SMON: enabling tx recovery”)。

剩下的唯一的问题是,这里的cache recovery是什么?显然它不是官方文档中所描述的”cache recovery”,几乎没有任何文档介绍存在这样一个recovery操作,这也是本文重点要介绍的。

我们来看另一个演示,这个演示用以说明cache recovery还存在于最普通的不包含Crash Recovery的数据库打开过程中:

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 1065353216 bytes
Fixed Size                  2089336 bytes
Variable Size             486542984 bytes
Database Buffers          570425344 bytes
Redo Buffers                6295552 bytes
Database mounted.
SQL> alter database open;
Database altered.
SQL> select * from v$version;
BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi
PL/SQL Release 10.2.0.4.0 - Production
CORE    10.2.0.4.0      Production
TNS for Linux: Version 10.2.0.4.0 - Production
NLSRTL Version 10.2.0.4.0 - Production
SQL> select * from global_name;
GLOBAL_NAME
--------------------------------------------------------------------------------
www.askmaclean.com
==================alert.log====================
alter database open
Tue Jun 14 18:43:52 2011
LGWR: STARTING ARCH PROCESSES
ARC0: Archival started
LGWR: STARTING ARCH PROCESSES COMPLETE
ARC0 started with pid=14, OS id=8133
Tue Jun 14 18:43:52 2011
Thread 1 opened at log sequence 1005
Current log# 3 seq# 1005 mem# 0: /flashcard/oradata/G10R2/onlinelog/o1_mf_3_6v34jpmp_.log
Current log# 3 seq# 1005 mem# 1: /s01/flash_recovery_area/G10R2/onlinelog/o1_mf_3_6v34jpyn_.log
Successful open of redo thread 1
Tue Jun 14 18:43:52 2011
ARC0: Becoming the 'no FAL' ARCH
ARC0: Becoming the 'no SRL' ARCH
ARC0: Becoming the heartbeat ARCH
Tue Jun 14 18:43:52 2011
SMON: enabling cache recovery
Tue Jun 14 18:43:53 2011
Successfully onlined Undo Tablespace 1.
Tue Jun 14 18:43:53 2011
SMON: enabling tx recovery
Database Characterset is UTF8
Opening with internal Resource Manager plan
where NUMA PG = 1, CPUs = 2
replication_dependency_tracking turned off (no async multimaster replication found)
Tue Jun 14 18:43:53 2011
Incremental checkpoint up to RBA [0x3ed.624.0], current log tail at RBA [0x3ed.944.0]
Tue Jun 14 18:43:53 2011
Starting background process QMNC
QMNC started with pid=15, OS id=8135
Tue Jun 14 18:43:53 2011
Completed: alter database open

因为是clean shutdown,所以这里不存在crash recovery。但这里同样出现了”SMON: enabling cache recovery”,可见cache recovery是每次实例启动instance startup必要执行的一种恢复操作。但问题是,这个恢复操作到底针对何种对象?

实际上cache recovery所要恢复的是rowcache,也就是我们常说的字典缓存(dictionary cache)。关于这个结论,肯定有很多人要问我这样说的依据是什么,对应于这个”cache recovery”的问题,我们很难从google中得到一些启示,因为它和官方文档所描述的”cache recovery-rolling forward”存在重名的关系。

为了证明cache recovery所恢复的是rowcache,我们需要一个实证,从正式的系统中得到验证。要做到这一点是比较困难的,我们需要Oracle愿意把整个database open的过程变成慢动作来供我们参考,验证要用到一些调试工具,例如gdb或者dbx。

我们首先将实例启动到mount状态,并对执行startup的LOCAL进程做gdb的breakpoint断点调试:

SQL> shutdown abort;
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 1065353216 bytes
Fixed Size                  2089336 bytes
Variable Size             486542984 bytes
Database Buffers          570425344 bytes
Redo Buffers                6295552 bytes
Database mounted.
找出LOCAL进程的系统进程号SPID
SQL> select spid from v$process
2  where addr in (
3  select paddr from v$session
4  where sid=(select distinct sid from v$mystat))
5  /
SPID
------------
8326
在实例startup nomount/mount后共享池的library cache就是可用的

SQL> select namespace from v$librarycache where gets!=0;
NAMESPACE
---------------
SQL AREA
TABLE/PROCEDURE
而rowcache则尚未被填充,因为字典缓存来源于自举对象(bootstrap$)和字典基表
SQL> select parameter,count,gets from v$rowcache where count!=0;
no rows selected
另开一个terminal窗口,并执行对LOCAL进程8326的gdb breakpoint调试
[oracle@rh2 ~]$ gdb $ORACLE_HOME/bin/oracle 8326
GNU gdb (GDB) Red Hat Enterprise Linux (7.0.1-23.el5)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
...
Reading symbols from /s01/db_1/bin/oracle...(no debugging symbols found)...done.
Attaching to program: /s01/db_1/bin/oracle, process 8326
Reading symbols from /s01/db_1/lib/libskgxp10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libskgxp10.so
Reading symbols from /s01/db_1/lib/libhasgen10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libhasgen10.so
Reading symbols from /s01/db_1/lib/libskgxn2.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libskgxn2.so
Reading symbols from /s01/db_1/lib/libocr10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libocr10.so
Reading symbols from /s01/db_1/lib/libocrb10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libocrb10.so
Reading symbols from /s01/db_1/lib/libocrutl10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libocrutl10.so
Reading symbols from /s01/db_1/lib/libjox10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libjox10.so
Reading symbols from /s01/db_1/lib/libclsra10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libclsra10.so
Reading symbols from /s01/db_1/lib/libdbcfg10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libdbcfg10.so
Reading symbols from /s01/db_1/lib/libnnz10.so...(no debugging symbols found)...done.
Loaded symbols for /s01/db_1/lib/libnnz10.so
Reading symbols from /usr/lib64/libaio.so.1...(no debugging symbols found)...done.
Loaded symbols for /usr/lib64/libaio.so.1
Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libdl.so.2
Reading symbols from /lib64/libm.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libm.so.6
Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.
[Thread debugging using libthread_db enabled]
Loaded symbols for /lib64/libpthread.so.0
Reading symbols from /lib64/libnsl.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnsl.so.1
Reading symbols from /lib64/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib64/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /lib64/libnss_files.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libnss_files.so.2
0x0000003181a0d8e0 in __read_nocancel () from /lib64/libpthread.so.0
输入断点kcrf_commit_force和kqlobjlod
(gdb) break kcrf_commit_force
Breakpoint 1 at 0x2724b6c
(gdb) break kqlobjlod
Breakpoint 2 at 0x1ac5e8c

在之前的terminal中执行数据库打开操作,因为breakpoint的关系这个open操作会hang住,
这时我们通过观察告警日志来了解恢复进度

SQL> alter database open;                              --这里会hang住
在gdb下输入continue,
(gdb) c
Continuing.
Breakpoint 1, 0x0000000002724b6c in kcrf_commit_force ()
观察告警日志可以发现redo application已经完成,但还未进入cache recovery阶段
alter database open
Tue Jun 14 19:14:33 2011
Beginning crash recovery of 1 threads
parallel recovery started with 2 processes
Tue Jun 14 19:14:33 2011
Started redo scan
Tue Jun 14 19:14:33 2011
Completed redo scan
39 redo blocks read, 74 data blocks need recovery
Tue Jun 14 19:14:33 2011
Started redo application at
Thread 1: logseq 1006, block 1155
Tue Jun 14 19:14:33 2011
Recovery of Online Redo Log: Thread 1 Group 1 Seq 1006 Reading mem 0
Mem# 0: /flashcard/oradata/G10R2/onlinelog/o1_mf_1_6v34jnkn_.log
Mem# 1: /s01/flash_recovery_area/G10R2/onlinelog/o1_mf_1_6v34jnst_.log
Tue Jun 14 19:14:33 2011
Completed redo application
Tue Jun 14 19:14:33 2011
Completed crash recovery at
Thread 1: logseq 1006, block 1194, scn 17200193
74 data blocks read, 74 data blocks written, 39 redo blocks read
Tue Jun 14 19:14:33 2011
LGWR: STARTING ARCH PROCESSES
ARC0: Archival started
LGWR: STARTING ARCH PROCESSES COMPLETE
ARC0 started with pid=17, OS id=8656
Tue Jun 14 19:14:33 2011
Thread 1 advanced to log sequence 1007 (thread open)
Thread 1 opened at log sequence 1007
Current log# 2 seq# 1007 mem# 0: /flashcard/oradata/G10R2/onlinelog/o1_mf_2_6v34jokt_.log
Current log# 2 seq# 1007 mem# 1: /s01/flash_recovery_area/G10R2/onlinelog/o1_mf_2_6v34jotq_.log
Successful open of redo thread 1
Tue Jun 14 19:14:33 2011
ARC0: Becoming the 'no FAL' ARCH
ARC0: Becoming the 'no SRL' ARCH
ARC0: Becoming the heartbeat ARCH
db_recovery_file_dest_size of 204800 MB is 6.81% used. This is a
user-specified limit on the amount of space that will be used by this
database for recovery-related files, and does not reflect the amount of
space available in the underlying filesystem or ASM diskgroup.
Tue Jun 14 19:14:37 2011
Incremental checkpoint up to RBA [0x3ef.3.0], current log tail at RBA [0x3ef.3.0]
且此时rowcache仍未被填充
SQL> select parameter,count,gets from v$rowcache where count!=0;
no rows selected

在gdb界面下再次执行continue 2次
(gdb) c
Continuing.
Breakpoint 1, 0x0000000002724b6c in kcrf_commit_force ()
(gdb) c
Continuing.
Breakpoint 2, 0x0000000001ac5e8c in kqlobjlod ()
观察告警日志可以发现已开始cache recovery,但也卡陷在cache recovery上,这保证我们的演示不受骚扰
Tue Jun 14 19:16:44 2011
SMON: enabling cache recovery
此时rowcache中出现唯一的一个dc_objects对象
select parameter,count,gets from v$rowcache where count!=0;
PARAMETER                             COUNT       GETS
-------------------------------- ---------- ----------
dc_objects                                1          1
这个对象是什么呢?也许你已经猜到了,我们做一个rowcache dump来看一下:
SQL> ALTER SESSION SET EVENTS 'immediate trace name row_cache level 10';
================row_cache trace===================
BUCKET 43170:
row cache parent object: address=0x92326060 cid=8(dc_objects)
hash=f3d1a8a1 typ=11 transaction=(nil) flags=00000001
own=0x92326130[0x9230f628,0x9230f628] wat=0x92326140[0x92326140,0x92326140] mode=S
status=EMPTY/-/-/-/-/-/-/-/-
set=0, complete=FALSE
data=
00000000 4f42000a 5453544f 24504152 00000000 00000000 00000000 00000000
00000000 00000001 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
BUCKET 43170 total object count=1
可以看到上述dc_objects尚未完成加载(status=EMPTY & complete=FALSE ),那么这是一个什么object呢?
4f42000a 5453544f 24504152 => 转换为文本即:OB TSTO$PAR也就是BOOTSTRAP$
换而言之在cache recovery时第一个恢复的字典缓存对象是BOOTSTRAP$,这并不出乎我们的意料。
启动实例的LOCAL进程的等待事件为instance state change,这是常规情况下我们观察不到得
SQL> select event,p1text,p1 from v$session where wait_class!='Idle';
EVENT                                    P1TEXT                                           P1
---------------------------------------- ---------------------------------------- ----------
instance state change                    layer                                             2
在gdb界面下再次continue,将载入更多的rowcache对象
(gdb) c
Continuing.
Breakpoint 2, 0x0000000001ac5e8c in kqlobjlod ()
BUCKET 37:
row cache parent object: address=0x916cd980 cid=3(dc_rollback_segments)
hash=5fed2a24 typ=9 transaction=(nil) flags=000000a6
own=0x916cda50[0x916cda50,0x916cda50] wat=0x916cda60[0x916cda60,0x916cda60] mode=N
status=VALID/INSERT/-/FIXED/-/-/-/-/-
data=
00000000 00000000 00000001 00000009 59530006 4d455453 00000000 00000000
00000000 00000000 00000000 00000000 00000003 00000000 00000000 00000000
00000000 00000000 00000000 00000000
BUCKET 37 total object count=1

595300064d455453 -> SYSTEM 属于dc_rollback_segments 也就是著名的system回滚段
BUCKET 55556:
row cache parent object: address=0x916d8cd0 cid=8(dc_objects)
hash=ce89d903 typ=11 transaction=(nil) flags=00000001
own=0x916d8da0[0x9230f628,0x9230f628] wat=0x916d8db0[0x916d8db0,0x916d8db0] mode=S
status=EMPTY/-/-/-/-/-/-/-/-
set=0, complete=FALSE
data=
00000000 5f430006 234a424f 00000000 00000000 00000000 00000000 00000000
00000000 00000005 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
00000000 00000000
BUCKET 55556 total object count=1

5f430006 234a424f -> C_OBJ# 是著名的bootstrap对象之一,可以从$ORACLE_HOME/rdbms/admin/sql.bsq中找到它
create rollback segment SYSTEM tablespace SYSTEM
storage (initial 50K next 50K)
/
create cluster c_obj# (obj# number)
pctfree 5 size 800                           /* don't waste too much space */
/* A table of 32 cols, 2 index, 2 col per index requires about 2K.
* A table of 10 cols, 2 index, 2 col per index requires about 750.
*/
storage (initial 130K next 200k maxextents unlimited pctincrease 0)
/* avoid space management during IOR I */
/

我们还可以通过v$rowcache_parent视图来了解dictionary cache的情况

SQL> col cache_name for a20
SQL> col keystr for a31
SQL> set linesize 200
SQL> select address,cache_name,existent,lock_mode,saddr,substr(key,1,30) keystr from v$rowcache_parent;
ADDRESS          CACHE_NAME           E  LOCK_MODE SADDR            KEYSTR
---------------- -------------------- - ---------- ---------------- -------------------------------
00000000916CCE20 dc_tablespaces       N          0 00               000000000000000000000000000000
00000000916CD980 dc_rollback_segments Y          0 00               000000000000000000000000000000
0000000092326060 dc_objects           Y          0 00               000000000A00424F4F545354524150
00000000916D8CD0 dc_objects           N          3 000000009BD91328 000000000600435F4F424A23000000
00000000916DA830 dc_object_ids        Y          0 00               380000000000000000000000000000

可以看到持有row cache lock的会话是'000000009BD91328',
且该dc_objects对象还处于non-existent状态,
换而言之真正装载rowcache的是启动实例的LOCAL服务进程
SQL> select sid,program,event,p1,p2,p3 from v$session where saddr='000000009BD91328';
SID PROGRAM                                          EVENT                                    P1   P2 P3
----- ------------------------------------------------ ---------------------------------------- -- ---- --
3294 sqlplus@rh2.oracle.com (TNS V1-V3)               db file scattered read                    1  378  3
该进程正在等待db file scattered read,fileid->1,block-378,这些块属于BOOTSTRAP$表

BOOTSTRAP$对象已从rowcache被载入到library cache中
SQL> select kglhdadr,kglnaobj from x$kglob where kglobtyp=2 and kglnaobj not like 'X$%';
KGLHDADR             KGLNAOBJ
-------------------- --------------------
0000000092326990     BOOTSTRAP$
SQL> select owner||'.'||Name from v$db_object_cache where type='TABLE' and name not like 'X$%';
OWNER||'.'||NAME
--------------------------------------------------------------------------------
SYS.BOOTSTRAP$

初步总结:

  1. 在数据库正式open前需要恢复字典缓存,这个步骤被称为cache recovery,其实是row cache recovery。与官方文档中描述的”cache recovery”不同,row cache recovery应当是Oracle Internal的叫法。
  2. 实际执行row cache recovery的不是SMON进程,而是启动实例的服务进程

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