本文主要是介绍TimesTen的守护进程，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
TimesTen的守护进程分为主守护进程和子守护进程。
主守护进程
主守护进程即ttDaemonAdmin启动的进程，也称为Data Manager Daemon。
主守护进程的作用为：
- Manages shared memory access
- Coordinates process recovery
- Keeps management statistics on what databases exist, which are in use, and which application processes are connected to which databases
- Manages RAM policy
- Starts replication processes, the TimesTen Server and the cache agent.
每一个TimesTen实例配有一个主守护进程，一个主守护进程下可有多个数据库。
子守护进程
每一个数据库/DataStore都配备相应的子守护进程(subdaemon), 子守护进程父进程即主守护进程。
在OS中可以查看到子守护进程，不过区别不明显，只能看到有两个实例tt1122和ttnew，其它的区别就是-id了:
$ ps -ef|grep timestensubd
oracle 2648 2644 0 Jun29 ? 00:02:35 /home/oracle/TimesTen/tt1122/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000000 -facility user
oracle 2649 2644 0 Jun29 ? 00:05:20 /home/oracle/TimesTen/tt1122/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000001 -facility user
oracle 2650 2644 0 Jun29 ? 00:00:35 /home/oracle/TimesTen/tt1122/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000002 -facility user
oracle 8775 2644 0 10:33 ? 00:00:13 /home/oracle/TimesTen/tt1122/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000011 -facility user
oracle 6633 6629 0 03:57 ? 00:00:25 /u01/TimesTen/ttnew/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000000 -facility user
oracle 6634 6629 0 03:57 ? 00:00:25 /u01/TimesTen/ttnew/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000001 -facility user
oracle 6635 6629 0 03:57 ? 00:00:25 /u01/TimesTen/ttnew/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000002 -facility user
oracle 6636 6629 0 03:57 ? 00:00:25 /u01/TimesTen/ttnew/bin/timestensubd -verbose -userlog tterrors.log -supportlog ttmesg.log -id 1000003 -facility user$ ps -p 2644PID TTY TIME CMD2644 ? 00:01:56 timestend$ ps -p 6629PID TTY TIME CMD6629 ? 00:00:51 timestend
从输出还可看出，2644和6629是主守护进程。
每一个timestensubd负责一个数据库。
$ ttstatus
TimesTen status report as of Thu Jun 30 17:56:03 2016Daemon pid 6629 port 55555 instance ttnew
TimesTen server pid 6638 started on port 55556
------------------------------------------------------------------------
Data store /u01/TimesTen/ttnew/info/DemoDataStore/repdb2_1122
There are no connections to the data store
Replication policy : Manual
Cache Agent policy : Manual
PL/SQL enabled.
------------------------------------------------------------------------
Accessible by group oracle
End of report
虽然没有任何数据库，表示之前看到的是idle subdaemon$ ttstatus
TimesTen status report as of Thu Jun 30 17:48:42 2016Daemon pid 2644 port 53392 instance tt1122
TimesTen server pid 2653 started on port 53393
------------------------------------------------------------------------
Data store /home/oracle/TimesTen/tt1122/info/DemoDataStore/cachedb2
There are 18 connections to the data store
Shared Memory KEY 0x0e0077ad ID 4718612
PL/SQL Memory KEY 0x0f0077ad ID 4751381 Address 0x7fa0000000
Type PID Context Connection Name ConnID
Process 10938 0x000000000203dad0 cachedb2 1
Replication 10955 0x00000000038aa750 LOGFORCE:1092778304 127
Replication 10955 0x0000000003910870 XLA_PARENT:1089628480 129
Replication 10955 0x0000000003925460 REPLISTENER:1101670720 131
Replication 10955 0x00000000039d8750 TRANSMITTER(M):1108805952 126
Replication 10955 0x00007fe9c00008c0 REPHOLD:1098090816 128
Replication 10955 0x00007fe9c80008c0 FAILOVER:1081899328 130
Subdaemon 2648 0x0000000001be0360 Manager 142
Subdaemon 2648 0x0000000001c57430 Rollback 141
Subdaemon 2648 0x0000000001debbc0 Checkpoint 137
Subdaemon 2648 0x0000000001e407f0 Monitor 136
Subdaemon 2648 0x0000000001e95420 IndexGC 135
Subdaemon 2648 0x000000000312f8f0 HistGC 139
Subdaemon 2648 0x0000000003184520 Log Marker 138
Subdaemon 2648 0x000000000325aa50 AsyncMV 134
Subdaemon 2648 0x00000000032af680 Aging 133
Subdaemon 2648 0x00000000033042b0 Deadlock Detector 132
Subdaemon 2648 0x00000000034097c0 Flusher 140
Replication policy : Manual
Replication agent is running.
Cache Agent policy : Manual
PL/SQL enabled.
------------------------------------------------------------------------
Data store /home/oracle/TimesTen/tt1122/info/DemoDataStore/repdb1_1122
There are no connections to the data store
Replication policy : Manual
Cache Agent policy : Manual
PL/SQL enabled.
------------------------------------------------------------------------
Data store /home/oracle/TimesTen/tt1122/info/DemoDataStore/cachedb1
There are 18 connections to the data store
Shared Memory KEY 0x4400c901 ID 3997713
PL/SQL Memory KEY 0x4500c901 ID 4030482 Address 0x7fa0000000
Type PID Context Connection Name ConnID
Process 11076 0x0000000001c84ad0 cachedb1 1
Replication 10918 0x000000000361f460 LOGFORCE:1101203776 127
Replication 10918 0x000000000368b270 REPHOLD:1108773184 130
Replication 10918 0x00000000036b2350 XLA_PARENT:1098053952 128
Replication 10918 0x00000000036c6f40 REPLISTENER:1093052736 129
Replication 10918 0x00000000038048e0 RECEIVER:1115072832 125
Replication 10918 0x00007fa0880008c0 FAILOVER:1083238720 131
Subdaemon 2649 0x0000000000e82360 Manager 142
Subdaemon 2649 0x0000000000ef9430 Rollback 141
Subdaemon 2649 0x0000000001008980 Monitor 136
Subdaemon 2649 0x000000000108d5e0 IndexGC 134
Subdaemon 2649 0x00000000010ff8f0 AsyncMV 133
Subdaemon 2649 0x0000000001134cd0 Flusher 132
Subdaemon 2649 0x0000000001272b40 Deadlock Detector 140
Subdaemon 2649 0x00000000012d6150 Log Marker 138
Subdaemon 2649 0x0000000001346c10 Checkpoint 137
Subdaemon 2649 0x000000000269bb80 HistGC 135
Subdaemon 2649 0x00000000026b0770 Aging 139
Replication policy : Manual
Replication agent is running.
Cache Agent policy : Manual
PL/SQL enabled.
------------------------------------------------------------------------
Accessible by group oracle
End of report$ ttstatus|grep -i subdaemon
Subdaemon 2648 0x0000000001be0360 Manager 142
Subdaemon 2648 0x0000000001c57430 Rollback 141
Subdaemon 2648 0x0000000001debbc0 Checkpoint 137
Subdaemon 2648 0x0000000001e407f0 Monitor 136
Subdaemon 2648 0x0000000001e95420 IndexGC 135
Subdaemon 2648 0x000000000312f8f0 HistGC 139
Subdaemon 2648 0x0000000003184520 Log Marker 138
Subdaemon 2648 0x000000000325aa50 AsyncMV 134
Subdaemon 2648 0x00000000032af680 Aging 133
Subdaemon 2648 0x00000000033042b0 Deadlock Detector 132
Subdaemon 2648 0x00000000034097c0 Flusher 140Subdaemon 2649 0x0000000000e82360 Manager 142
Subdaemon 2649 0x0000000000ef9430 Rollback 141
Subdaemon 2649 0x0000000001008980 Monitor 136
Subdaemon 2649 0x000000000108d5e0 IndexGC 134
Subdaemon 2649 0x00000000010ff8f0 AsyncMV 133
Subdaemon 2649 0x0000000001134cd0 Flusher 132
Subdaemon 2649 0x0000000001272b40 Deadlock Detector 140
Subdaemon 2649 0x00000000012d6150 Log Marker 138
Subdaemon 2649 0x0000000001346c10 Checkpoint 137
Subdaemon 2649 0x000000000269bb80 HistGC 135
Subdaemon 2649 0x00000000026b0770 Aging 139
主守护进程可以按需动态产生subdaemon。当有数据库需要加载到内存时，就会产生新的或使用已有的idle subdaemon来负责这个数据库。
TimesTen总是预留一个idle的subdaemon：
a) 主daemon启动时, 会附带启动4 subdaemon，并且最初的状态为idle
b) 若有数据库需要加载到内存，则会指派一个subdaemon负责一个数据库，但总会预留一个idle的subdaemon。
缺省启动的subdaemon数量可以在ttendaemon.options中通过-minsubs设置。
subdaemon的作用包括：
1. 将数据库从内存中卸载
2. 将Log buffer中的日志写盘
3. 日志的归档和清理
4. 检查和消除死锁
5. 在数据库非正常关闭时，从checkpoint和log文件中恢复
6. 回退交易
7. 实现缓存Aging
常用的subdaemon包括：
Worker: Periodically checks for deadlocks and canceling SQL operations on behalf of other applications in order to break any deadlocks.
Flusher: Flushes contents of Log buffer to disk
Checkpoint: Performs checkpoint operation.
Monitor: Implements lock wait timeout. For more information, please refer connection attribute “LockWait” in “Oracle TimesTen In-Memory Database API Reference Guide”.
HistGC: Purging rows in internal tables SYS.TABLE_HISTORY and SYS.COLUMN_HISTORY periodically when they are no longer needed by XLA readers.
Aging: Implementing the aging policies of various tables.
参考
- TimesTen subdaemon: Frequently Asked Questions (Doc ID 759437.1)
- TimesTen recovery from abnormally terminated connections (Doc ID 759443.1)
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