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When Will instance recovery be generated after in-depth analysis of instance recovery? When your database server suffers an abnormal power failure, instance recovery will occur when you restart the database. Instance recovery is automatically completed by the database without DBA interference. Of course, there is a premise: data files, online log files, and control files must not be damaged. Let's use an experiment to analyze the whole process of instance recovery! 1. Before shutting down the da
background processes if necessary.· Register an Oracle instance with the Oracle TNS Listener 2.SMON: System Monitor(System Monitor)· Clear temporary space· Merge free spaceIf you are using a dictionary-managed tablespace, SMON is responsible for obtaining consecutive idle segments in the tablespace and merging them into a larger idle segment.· Recover the transaction for the original unavailable files: This is similar to the role of SMON when the database is started· Restore instances of failed
The principle of instance recovery when the database suddenly crashes, it is not time to refresh the dirty data blocks in the buffer cache to the data file, at the same time, when a transaction is suddenly interrupted when the instance crashes, the transaction is in the intermediate state, that is, neither commit nor rollback. At this time, the content in the data file cannot reflect the status of the instance crash. In this way, the closed database is inconsistent. The next time you start an in
Oracle architecture learning notes: the most important thing for oracledatabase is onlineredolog, ldquo; write rdquo;: Checkpoint Process computing workload to set checkpoints, Oracle architecture learning notes, the most important of oracle database is online redo log, ldquo; write rdquo;: Checkpoint Process computing workload, to determine the checkpoint,
not become the bottleneck of HDFS operations, hadoop adopts the following method: No snapshot of the current file system is persisted, the list of HDFS operations in the recent period will be saved to an editlog file in namenode. When the namenode is restarted, in addition to the load fsimage accident, the HDFS operation recorded in the editlog file will be replaced to restore the final state before the HDFS restart. Secondarynamenode periodically merges the HDFS operations recorded in the edi
1. Meta Data Management OverviewHDFs metadata, grouped by type, consists mainly of the following sections:1, the file, the directory of its own property information, such as file name, directory name, modify information and so on.2. Storing information about the information stored in the file, such as block information, block case, number of copies, etc.3, records the Datanode of HDFs information, for Datanode management.In the form of memory metadata and metadata files two, respectively, there
I. When do I need instance recovery? In shutdown normal or shutdown immediate, the so-called clean shutdown will automatically trigger the checkpoint and write the SCN record back. When a checkpoint occurs, the SCN is written to four places: Three places are in the control file: (1) SYSTEM CHECKPOINT SCN (2) Datafile checkpoi
Data | database Working diagram of a transaction Transactions ensure the consistency and recoverability of data. The transaction works as shown in Figure 1. Figure 1 Working schematic diagram of a transaction After the transaction starts, all the operations of the Office are written to the transaction log in succession. There are generally two types of operations written to the log: one for data manipulation and one for task operations. Operations on data, such as insertions, deletions
write IO线程数（innodb 1.0x） purge thread ： 事务提交后，其所使用的undolog就不再需要，所以需要存储引擎负责回收并分配新undo页； innodb1.1x之前 purge动作在master thread中完成； 之后可以通过配置 innodb_purge_threads=1 开启独立的purge thread来处理，以减轻master thread负担，提高CPU使用率； page cleaner thread : innodb1.2x版本开始，将脏页刷新操作放在单独的page cleaner thread中，进一步减轻了master thread负担，并减轻用户查询线程的阻塞；Buffer pool缓冲池： 缓冲池本质上就是一块内存区域，通过内存的速度弥补磁盘速度较慢对数据库性能的影响； 在数据库中进行读取操作时，首先判断待读取页是否存在缓冲池中； 如果存在，则缓冲池命中，直接从缓冲池中读取进行后续操作； 否则进行io操作，从磁盘中读取页，然后存
it is monitoring the database, it is rarely necessary for an administrator to recover from an instance failure. When a DB instance fails, Oracle Restart attempts to restart the instance. If manual intervention is required, there may be a more serious problem preventing the instance from restarting, such as a memory CPU failure. Understanding Instance Recovery: Checkpoint (CKPT) session To understand instance recovery, you need to unders
Oracle Learning--buffer Cache in-depth analysis650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/40/BE/wKioL1PPVxOwPpjTAAL_LJN_ltc591.jpg "title=" 1.png " alt= "Wkiol1ppvxowppjtaal_ljn_ltc591.jpg"/>Server process and database buffer cache:When a block is required by the server, the block needs to be read by series steps:1. First, the server uses a hash function to check whether the required blocks can be obtained from the buffer cache. If a buffer is found, it is moved to the LRU list
V $ database. CONTROLFILE_CHANGE # (indicates the last scn Number of the control file recovered from the backup. If the control file is not V $ database. CONTROLFILE_CHANGE # (indicates the last scn Number of the control file recovered from the backup. If the control file is not V $ database. CHECKPOINT_CHANGE # (last scn checkpointed)V $ database. CONTROLFILE_SEQUENCE # (control file sequence number incremented by control file transactions)V $ database. CONTROLFILE_CHANGE # (last scn in back
entries. This delay improves data writing performance, such as batch effects. Similar to Redo Log Buffer, Redo Log File is also used cyclically. Oracle allows at least two Log groups. By default, three log groups are created during database creation. Sys @ NEI> select group #, members, status from v $ log; GROUP # members status ------------ ------------------ 1 1 INACTIVE 2 1 CURRENT 3 1 INACTIVE when a log file is full, switch to another Log file, which is called Log Switch. Log Switch trigge
data in batches.Similar to redo log buffer, redo log file is also used cyclically. Oracle allows at least two log groups. By default, three log groups are created during database creation.SQL> select group #, members, status from V $ log; Group # members status------------------------------------1 1 inactive2 1 Current3 1 inactiveWhen a log file is fully written, it is switched to another log file, which is called a log switch. Log switch triggers a checkpo
V $ database. CHECKPOINT_CHANGE # (last scn checkpointed)V $ database. CONTROLFILE_SEQUENCE # (control file sequence number incremented by control file transactions)V $ database. CONTROLFILE_CHANGE # (last scn in backup control file; null if the control file is not a backup)V $ datafile. CHECKPOINT_CHANGE # (scn at last checkpoint)V $ datafile_header. CHECKPOINT_CHANGE # (datafile checkpoint change #V $ log
SCN is the internal clock of Oracle, which is used to reflect changes in the database and is constantly updated during operation. SCN types include: SCN is the internal clock of Oracle, which is used to reflect changes in the database and is constantly updated during operation. SCN types include: SCN is the internal clock of Oracle, which is used to reflect changes in the database and is constantly updated during operation. SCN types include: (1) Current SCN OF THE SYSTEM (2)
A checkpoint is actually a record of past history and can be considered as a log. however, this is simplified. for example, I have another piece of text. there are a pile of links in the text. my current task is to download the content from those addresses. in addition, due to network problems or website problems, each download may not be very successful. A chain disconnection or socket Exception error may occur. However, no matter what kind of errors
multiple online redo logs and place them on separate disks, and it is recommended that you store multiple backups on the same disk, even if you cannot put them on multiple disks, to avoid I/O failure. The multiplexing of online redo logs can affect performance, but the priority of the database is reliability. 650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M00/4A/5E/wKioL1QkeFrBjY5TAAGfKL36Qqc284.jpg "title=" 6.png " alt= "Wkiol1qkefrbjy5taagfkl36qqc284.jpg"/>Members of a group should be
sequence number when a dirty page is modified, and also to record checkpoint, which, through the LSN, can be specifically located in the Redo log file.To manage the dirty pages, the page on each instance in Buffer Pool is maintained on a flush List,flush list, sorted by the LSN number in which the page was modified. So when doing redo checkpoint periodically, the LSN of choice is always the oldest page on
acting on the buffer, and then dbwn will dump the dirty buffers into the disk. When does Dbwn write? Dbwn is a lazy process that writes as little as possible , in the following four cases it performs writes: A. There is no buffer available (you have to write it) B. Too many dirty buffers C.3 seconds Timeout (writes are performed once at the latest 3 seconds) D. A checkpoint, checkpoint (
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