外文翻譯---解析oracle數(shù)據(jù)庫后臺進程的功能

1、<p>　　耿祥義.JSP 基礎教程.北京:清華大學出版社,2009.10</p><p><b>　　附錄</b></p><p><b>　　英文原文</b></p><p>　　Analysis of Oracle database background process function</p>

2、<p>　　1.DBWR process: the process of the implementation of the buffer is written to the data file, is responsible for the buffer memory management in a Oracle background process. When a buffer buffer is modified,

3、it is marked as" dirty", DBWR is the main task of" dirty" buffer is written to disk, so that the buffer to maintain" clean". Because the buffer memory buffer in the database or user process

4、dirty, unused buffer to reduce the number of. When the unused buffer down to little, so that user proce</p><p>　　Oracle uses LRU ( LEAST RECENTLY USED ) algorithm ( LRU ) keep the memory data block is a rece

5、ntly used, so that the I/O minimum. In the following case indicates that DBWR will dirty buffers to disk:</p><p>　　When a server process will be a buffer into the" dirty" table, the dirty expressio

6、n to the critical length, the service will notify DBWR writing. The critical length for the value of the parameter DB-BLOCK-WRITE-BATCH half.</p><p>　　When a server process in a LRU look-up table in DB-BLOCK

7、-MAX-SCAN-CNT buffer, did not find unused buffer, it stops to find and notify the DBWR to write. Timeout ( every3 seconds ), DBWR will inform itself. When a checkpoint, LGWR will inform DBWR. of the first two cases, DBWR

8、 will dirty table block is written to disk, each can write blocks by the initialization parameter DB-BLOCK- specified by WRITE-BATCH. If the dirty list without this parameter specifies the number of buffer, DBWR from the

9、 LUR</p><p>　　If the DBWR in three inactive, a time-out occurs. In this case the DBWR on the LRU table to find the specified number of buffer, to find any dirty buffers to disk. Whenever a timeout occurs, DB

10、WR finds a new buffer group. Each time by the DBWR to find the number of buffers for sleep parameter DB-BLOCK- WRITE-BATCH values two times. If the database is idle, DBWR will eventually all buffer storage to disk.</p

11、><p>　　In the occurs check point, LGWR specifies a modified buffer table must be written to disk. DBWR the specified buffer is written to disk.</p><p>　　On some platforms, one instance can have mul

12、tiple DBWR. in this instance, some blocks can be written to a disk, some other piece can be written to other disk. The parameter DB-WRITERS control of DBWR process number.</p><p>　　2. LGWR process: the proce

13、ss will log buffer is written to disk in a log file, it is responsible for the management of log buffer of a Oracle background process. LGWR process will since the last written to disk since all log entries for output, t

14、he output of the LGWR:</p><p>　　◆When a user process to submit a written when a commit record transaction.</p><p>　　◆Every three seconds will log buffer output.</p><p>　　◆When the l

15、og buffer1/3 is full when the log buffer output.</p><p>　　◆When DBWR will modify the buffer is written to disk when the log buffer output.</p><p>　　The LGWR process synchronous writes to the act

16、ive mirror online log file group. If the group a file to be deleted or not available, LGWR can continue to write to the group and other documents.</p><p>　　Log buffer is a circular buffer. When the LGWR log

17、buffer log entries are written to the log file, the server process can be a new log entry is written to the log buffer. LGWR used to write very quickly, can ensure that the log buffer total space can be written into the

18、new log entries.</p><p>　　Note: sometimes when we need more log buffer, LWGR in a transaction log entries before will write log entries, and these only when in the future after the transaction commits to per

19、manent.</p><p>　　ORACLE uses fast delivery mechanism, when the user issues a COMMIT statement, an COMMIT record immediately into the log buffer, but the corresponding data buffer change is to be delayed, unt

20、il more effective only when they are written to the data file. When a transaction is committed, is assigned to a system change number (SCN ), which together with the transaction log records in the log. Because the SCN re

21、corded in the log, so that in the parallel server configuration, recovery operations can b</p><p>　　3. CKPT process: the process at the inspection point appears, all the data file headers are modified, indic

22、ating the check point. Usually, the task performed by LGWR. However, if the check point significantly degrade the system performance, the CKPT process running, from the original LGWR process of the implementation of the

23、checkpoint job separated, by the CKPT process to achieve. For many applications, the CKPT process is not necessary. Only when the database has many data files, LGWR in check</p><p>　　The initialization param

24、eter CHECKPOINT-PROCESS control of CKPT process that can or not. The default for FALSE, namely, that can't.</p><p>　　4. SMON process: the process instance startup, perform instance recovery, is also resp

25、onsible for cleaning up no longer use temporary segments. In a parallel server environment, SMON on fault CPU or instance instance recovery. The SMON process is regularly called up, check is needed, or other process that

26、 needs to be invoked.</p><p>　　5. PMON process: the process in a user process failure recovery implementation process, responsible for the cleaning of memory storage area and release the resources used by th

27、e process. Example: it is to reset the events table status, releasing the blockade, the failure process of ID from activity in the process table remove. PMON also periodically checks the scheduling process ( DISPATCHER )

28、 and a server process state, if the dead, then restart ( not including intentional deletion process ).</p><p>　　PMON regularly called up, check is needed, or other process that needs to be invoked.</p>

29、<p>　　6. RECO process: the process is in a distributed option when used by a process, automatic solution in the distributed transaction failure. A node RECO background process automatically connect to include othe

30、r be in suspense distributed transaction database, RECO automatically solve all pending and affairs. Any corresponding to the processed is pending transaction is one from each database table delete suspended matters.<

31、/p><p>　　When a database server RECO background process attempts to establish a remote server, if the remote server is not available or network connection cannot be established, RECO automatically at a time int

32、erval after connect again.</p><p>　　RECO background process only when allows distributed transaction system, and DISTRIBUTED C TRANSACTIONS parameter is greater than 0.</p><p>　　7. ARCH process:

33、 the process will have to fill the online log files are copied to the specified storage device. When the log is ARCHIVELOG use, and can automatically archiving ARCH process exists.</p><p>　　8. The LCKn proce

34、ss is: with parallel server option environment, can be up to10 processes ( LCK0, LCK1... ... For example, LCK9), the block between the.</p><p>　　9. ( Dnnn process scheduling process ): the process allows the

35、 user process shared limited server process ( SERVER PROCESS ). No scheduling process, each user process requires a dedicated server process ( DEDICATEDSERVER PROCESS ). Multi-threaded server ( MULTI-THREADED SERVER ) ca

36、n support multiple user processes. If the system has a large number of users, many cues server can support a large users, especially in _ client server environment.</p><p>　　In a database instance can set up

37、 multiple scheduling process. For each kind of network protocol to establish at least one dispatcher processes. Database administrator according to the operating system of each process can be connected with restrictions

38、on the number of decisions to initiate the scheduler optimal number, when the instance is running can be added to or deleted from the scheduling process. Multiple cue server requires SQL*NET version 2 or later version. I

39、n a multiple cue server con</p><p><b>　　中文譯文</b></p><p>　　解析Oracle數(shù)據(jù)庫后臺進程的功能</p><p>　　1、DBWR進程：該進程執(zhí)行將緩沖區(qū)寫入數(shù)據(jù)文件，是負責緩沖存儲區(qū)管理的一個Oracle后臺進程。當緩沖區(qū)中的一緩沖區(qū)被修改，它被標志為“弄臟”，DBWR的主要任務是

40、將“弄臟”的緩沖區(qū)寫入磁盤，使緩沖區(qū)保持“干凈”。由于緩沖存儲區(qū)的緩沖區(qū)填入數(shù)據(jù)庫或被用戶進程弄臟，未用的緩沖區(qū)的數(shù)目減少。當未用的緩沖區(qū)下降到很少，以致用戶進程要從磁盤讀入塊到內存存儲區(qū)時無法找到未用的緩沖區(qū)時，DBWR將管理緩沖存儲區(qū)，使用戶進程總可得到未用的緩沖區(qū)。 </p><p>　　Oracle采用LRU（LEAST RECENTLY USED）算法（最近最少使用算法）保持內存中的數(shù)據(jù)塊是最近使用的，

41、使I/O最小。在下列情況預示DBWR 要將弄臟的緩沖區(qū)寫入磁盤： </p><p>　　當一個服務器進程將一緩沖區(qū)移入“弄臟”表，該弄臟表達到臨界長度時，該服務進程將通知DBWR進行寫。該臨界長度是為參數(shù)DB-BLOCK-WRITE-BATCH的值的一半。 </p><p>　　當一個服務器進程在LRU表中查找DB-BLOCK-MAX-SCAN-CNT緩沖區(qū)時，沒有查到未用的緩沖區(qū)，它停止

42、查找并通知DBWR進行寫。出現(xiàn)超時（每次3秒），DBWR 將通知本身。當出現(xiàn)檢查點時，LGWR將通知DBWR.在前兩種情況下，DBWR將弄臟表中的塊寫入磁盤，每次可寫的塊數(shù)由初始化參數(shù)DB-BLOCK- WRITE-BATCH所指定。如果弄臟表中沒有該參數(shù)指定塊數(shù)的緩沖區(qū)，DBWR從LUR表中查找另外一個弄臟緩沖區(qū)。 </p><p>　　如果DBWR在三秒內未活動，則出現(xiàn)超時。在這種情況下DBWR對LRU表查找

43、指定數(shù)目的緩沖區(qū)，將所找到任何弄臟緩沖區(qū)寫入磁盤。每當出現(xiàn)超時，DBWR查找一個新的緩沖區(qū)組。每次由DBWR查找的緩沖區(qū)的數(shù)目是為寢化參數(shù)DB-BLOCK- WRITE-BATCH的值的二倍。如果數(shù)據(jù)庫空運轉，DBWR最終將全部緩沖區(qū)存儲區(qū)寫入磁盤。 </p><p>　　在出現(xiàn)檢查點時，LGWR指定一修改緩沖區(qū)表必須寫入到磁盤。DBWR將指定的緩沖區(qū)寫入磁盤。 </p><p>　　在有

44、些平臺上，一個實例可有多個DBWR.在這樣的實例中，一些塊可寫入一磁盤，另一些塊可寫入其它磁盤。參數(shù)DB-WRITERS控制DBWR進程個數(shù)。 </p><p>　　2、LGWR進程：該進程將日志緩沖區(qū)寫入磁盤上的一個日志文件，它是負責管理日志緩沖區(qū)的一個Oracle后臺進程。LGWR進程將自上次寫入磁盤以來的全部日志項輸出，LGWR輸出： </p><p>　　◆當用戶進程提交一事務時寫

45、入一個提交記錄。 </p><p>　　◆每三秒將日志緩沖區(qū)輸出。 </p><p>　　◆當日志緩沖區(qū)的1/3已滿時將日志緩沖區(qū)輸出。 </p><p>　　◆當DBWR將修改緩沖區(qū)寫入磁盤時則將日志緩沖區(qū)輸出。</p><p>　　LGWR進程同步地寫入到活動的鏡象在線日志文件組。如果組中一個文件被刪除或不可用，LGWR可繼續(xù)地寫入該組的

46、其它文件。 </p><p>　　日志緩沖區(qū)是一個循環(huán)緩沖區(qū)。當LGWR將日志緩沖區(qū)的日志項寫入日志文件后，服務器進程可將新的日志項寫入到該日志緩沖區(qū)。LGWR 通常寫得很快，可確保日志緩沖區(qū)總有空間可寫入新的日志項。 </p><p>　　注意：有時候當需要更多的日志緩沖區(qū)時，LWGR在一個事務提交前就將日志項寫出，而這些日志項僅當在以后事務提交后才永久化。 </p>&l

47、t;p>　　ORACLE使用快速提交機制，當用戶發(fā)出COMMIT語句時，一個COMMIT記錄立即放入日志緩沖區(qū)，但相應的數(shù)據(jù)緩沖區(qū)改變是被延遲，直到在更有效時才將它們寫入數(shù)據(jù)文件。當一事務提交時，被賦給一個系統(tǒng)修改號（SCN），它同事務日志項一起記錄在日志中。由于SCN記錄在日志中，以致在并行服務器選項配置情況下，恢復操作可以同步。 </p><p>　　3、CKPT進程：該進程在檢查點出現(xiàn)時，對全部數(shù)據(jù)文

48、件的標題進行修改，指示該檢查點。在通常的情況下，該任務由LGWR執(zhí)行。然而，如果檢查點明顯地降低系統(tǒng)性能時，可使CKPT進程運行，將原來由LGWR進程執(zhí)行的檢查點的工作分離出來，由CKPT進程實現(xiàn)。對于許多應用情況，CKPT進程是不必要的。只有當數(shù)據(jù)庫有許多數(shù)據(jù)文件，LGWR在檢查點時明顯地降低性能才使CKPT運行。 CKPT進程不將塊寫入磁盤，該工作是由DBWR完成的。</p><p>　　初始化參數(shù)CHECK

49、POINT-PROCESS控制CKPT進程的使能或使不能。缺省時為FALSE，即為使不能。 </p><p>　　4、SMON進程：該進程實例啟動時，執(zhí)行實例恢復，還負責清理不再使用的臨時段。在具有并行服務器選項的環(huán)境下，SMON對有故障CPU或實例進行實例恢復。SMON進程有規(guī)律地被呼醒，檢查是否需要，或者其它進程發(fā)現(xiàn)需要時可以被調用。 </p><p>　　5、PMON進程：該進程在用

50、戶進程出現(xiàn)故障時執(zhí)行進程恢復，負責清理內存儲區(qū)和釋放該進程所使用的資源。例：它要重置活動事務表的狀態(tài)，釋放封鎖，將該故障的進程的ID從活動進程表中移去。PMON還周期地檢查調度進程（DISPATCHER）和服務器進程的狀態(tài)，如果已死，則重新啟動（不包括有意刪除的進程）。 </p><p>　　6、RECO進程：該進程是在具有分布式選項時所使用的一個進程，自動地解決在分布式事務中的故障。一個結點RECO后臺進程自動

51、地連接到包含有懸而未決的分布式事務的其它數(shù)據(jù)庫中，RECO自動地解決所有的懸而不決的事務。任何相應于已處理的懸而不決的事務的行將從每一個數(shù)據(jù)庫的懸掛事務表中刪去。 </p><p>　　當一數(shù)據(jù)庫服務器的RECO后臺進程試圖建立同一遠程服務器的通信，如果遠程服務器是不可用或者網(wǎng)絡連接不能建立時，RECO自動地在一個時間間隔之后再次連接。 </p><p>　　RECO后臺進程僅當在允許分布

52、式事務的系統(tǒng)中出現(xiàn)，而且DISTRIBUTED C TRANSACTIONS參數(shù)是大于0。 </p><p>　　7、ARCH進程：該進程將已填滿的在線日志文件拷貝到指定的存儲設備。當日志是為ARCHIVELOG使用方式、并可自動地歸檔時ARCH進程才存在。 </p><p>　　8、LCKn進程：是在具有并行服務器選件環(huán)境下使用，可多至10個進程（LCK0，LCK1……，LCK9），用于

53、實例間的封鎖。 </p><p>　　9、Dnnn進程（調度進程）：該進程允許用戶進程共享有限的服務器進程（SERVER PROCESS）。沒有調度進程時，每個用戶進程需要一個專用服務進程（DEDICATEDSERVER PROCESS）。對于多線索服務器（MULTI-THREADED SERVER）可支持多個用戶進程。如果在系統(tǒng)中具有大量用戶，多線索服務器可支持大量用戶，尤其在客戶_服務器環(huán)境中。 </p

54、><p>　　在一個數(shù)據(jù)庫實例中可建立多個調度進程。對每種網(wǎng)絡協(xié)議至少建立一個調度進程。數(shù)據(jù)庫管理員根據(jù)操作系統(tǒng)中每個進程可連接數(shù)目的限制決定啟動的調度程序的最優(yōu)數(shù)，在實例運行時可增加或刪除調度進程。多線索服務器需要SQL*NET版本2或更后的版本。在多線索服務器的配置下，一個網(wǎng)絡接收器進程等待客戶應用連接請求，并將每一個發(fā)送到一個調度進程。如果不能將客戶應用連接到一調度進程時，網(wǎng)絡接收器進程將啟動一個專用服務器進程

55、。該網(wǎng)絡接收器進程不是Oracle實例的組成部分，它是處理與Oracle有關的網(wǎng)絡進程的組成部分。在實例啟動時，該網(wǎng)絡接收器被打開，為用戶連接到Oracle建立一通信路徑，然后每一個調度進程把連接請求的調度進程的地址給予它的接收器。當一個用戶進程作連接請求時，網(wǎng)絡接收器進程分析請求并決定該用戶是否可使用一調度進程。如果是，該網(wǎng)絡接收器進程返回該調度進程的地址，之后用戶進程直接連接到該調度進程。有些用戶進程不能調度進程通信（如果使用SQL