怎么理解I/O性能

本篇內(nèi)容主要講解“怎么理解I/O性能”，感興趣的朋友不妨來看看。本文介紹的方法操作簡(jiǎn)單快捷，實(shí)用性強(qiáng)。下面就讓小編來帶大家學(xué)習(xí)“怎么理解I/O性能”吧!

為了理解I/O性能，你必須要詳細(xì)了解存儲(chǔ)文件的存儲(chǔ)層次信息。Oracle提供了一組動(dòng)態(tài)性能視國(guó)來顯示文件到邏輯卷中間層到實(shí)際的物理設(shè)備之間的映射信息。使用這些動(dòng)態(tài)性能視圖，可以找到一個(gè)文件的任何數(shù)據(jù)塊所內(nèi)置的實(shí)際物理磁盤。Oracle數(shù)據(jù)庫使用一個(gè)名叫FMON的后臺(tái)進(jìn)程來管理映射信息。Oracle提供了PL/SQL dbms_storage_map包來將映射操作填充到映射視圖中。Oracle數(shù)據(jù)庫文件映射當(dāng)映射Oracle ASM文件時(shí)不需要使用第三方的動(dòng)態(tài)庫。另外，Oracle數(shù)據(jù)庫支持在所有操作系統(tǒng)平臺(tái)上對(duì)Oracle ASM文件的映射。

對(duì)Oracle ASM文件啟用文件映射
為了啟用文件映射，需要將參數(shù)file_mapping設(shè)置為true。數(shù)據(jù)庫實(shí)例不必關(guān)閉來設(shè)置這個(gè)參數(shù)。可以使用以下alter system語句來設(shè)置這個(gè)參數(shù):

SQL> alter system set file_mapping=true scope=both sid='*';
System altered.

執(zhí)行合適的dbms_storage_map映射過程
.在冷啟動(dòng)情況下，Oracle數(shù)據(jù)庫在剛剛啟動(dòng)時(shí)沒有映射操作被調(diào)用?？梢詧?zhí)行dbms_storage_map.map_all過程來為數(shù)據(jù)庫相關(guān)的整個(gè)I/O子系統(tǒng)來構(gòu)建映射信息。例如，下面的命令構(gòu)建映射信息并且提供10000事件:

SQL> execute dbms_storage_map.map_all(10000);
PL/SQL procedure successfully completed.

.在暖啟動(dòng)情況下，Oracle數(shù)據(jù)庫已經(jīng)構(gòu)建了映射信息，可以選擇執(zhí)行dbms_storage_map.map_save過程來將映射信息保存在數(shù)據(jù)字典中。缺省情況下這個(gè)過程將被dbms_storage_map.map_all過程調(diào)用，這將強(qiáng)制SGA中的所有映射信息被刷新到磁盤。缺省情況下dbms_storage_map.map_save過程將被dbms_storage_map.map_all()。在重啟數(shù)據(jù)庫后，使用dbms_storage_map.restore()過程來還原映射信息到SGA中。如果需要，dbms_storage_map.map_all()可以用來刷新映射信息。

由dbms_storage_map包生成的映射信息會(huì)被捕獲到動(dòng)態(tài)性能視圖中。這些視圖包括v$map_comp_list,v$map_element,v$map_ext_element,v$map_file,v$map_file_extent,v$map_file_io_stack,v$map_library與v$map_subelement。
可以使用v$map_file來查詢文件映射信息:

SQL> select file_map_idx, substr(file_name,1,45), file_type, file_structure from v$map_file;
FILE_MAP_IDX SUBSTR(FILE_NAME,1,45)                                                                     FILE_TYPE   FILE_STRU
------------ ------------------------------------------------------------------------------------------ ----------- ---------
           0 +DATA/CS/DATAFILE/system.272.970601831                                                     DATAFILE    ASMFILE
           1 +DATA/CS/DATAFILE/sysaux.273.970601881                                                     DATAFILE    ASMFILE
           2 +DATA/CS/DATAFILE/undotbs1.274.970601905                                                   DATAFILE    ASMFILE
           3 +DATA/CS/4700A987085B3DFAE05387E5E50A8C7B/DAT                                              DATAFILE    ASMFILE
           4 +DATA/CS/4700A987085B3DFAE05387E5E50A8C7B/DAT                                              DATAFILE    ASMFILE
           5 +DATA/CS/DATAFILE/users.275.970601909                                                      DATAFILE    ASMFILE
           6 +DATA/CS/4700A987085B3DFAE05387E5E50A8C7B/DAT                                              DATAFILE    ASMFILE
           7 +DATA/CS/DATAFILE/undotbs2.284.970602381                                                   DATAFILE    ASMFILE
           8 +DATA/CS/DATAFILE/test.326.976211663                                                       DATAFILE    ASMFILE
           9 +DATA/CS/DATAFILE/jy.331.976296525                                                         DATAFILE    ASMFILE
          10 +DATA/CS/6C61AD7B443C2CD2E053BE828A0A2A74/DAT                                              DATAFILE    ASMFILE
          11 +DATA/CS/6C61AD7B443C2CD2E053BE828A0A2A74/DAT                                              DATAFILE    ASMFILE
          12 +DATA/CS/6C61AD7B443C2CD2E053BE828A0A2A74/DAT                                              DATAFILE    ASMFILE
          13 +DATA/CS/ONLINELOG/group_2.277.970601985                                                   LOGFILE     ASMFILE
          14 +DATA/CS/ONLINELOG/group_1.278.970601985                                                   LOGFILE     ASMFILE
          15 +DATA/CS/ONLINELOG/group_3.285.970602759                                                   LOGFILE     ASMFILE
          16 +DATA/CS/ONLINELOG/group_4.286.970602761                                                   LOGFILE     ASMFILE
          17 +DATA/CS/ONLINELOG/redo05.log                                                              LOGFILE     ASMFILE
          18 +DATA/CS/ONLINELOG/redo06.log                                                              LOGFILE     ASMFILE
          19 +DATA/CS/ONLINELOG/redo07.log                                                              LOGFILE     ASMFILE
          20 +DATA/CS/ONLINELOG/redo08.log                                                              LOGFILE     ASMFILE
          21 +DATA/CS/ONLINELOG/redo09.log                                                              LOGFILE     ASMFILE
          22 +DATA/CS/ONLINELOG/redo10.log                                                              LOGFILE     ASMFILE
          23 +DATA/CS/TEMPFILE/temp.279.970602003                                                       TEMPFILE    ASMFILE
          24 +DATA/CS/67369AA1C9AA3E71E053BE828A0A8262/TEM                                              TEMPFILE    ASMFILE
          25 +DATA/CS/6C61AD7B443C2CD2E053BE828A0A2A74/TEM                                              TEMPFILE    ASMFILE
          26 +DATA/arch/1_222_970601983.dbf                                                             ARCHIVEFILE ASMFILE
          27 +DATA/arch/1_223_970601983.dbf                                                             ARCHIVEFILE ASMFILE
          28 +DATA/arch/2_277_970601983.dbf                                                             ARCHIVEFILE ASMFILE
          29 +DATA/arch/2_278_970601983.dbf                                                             ARCHIVEFILE ASMFILE
          30 +DATA/arch/2_279_970601983.dbf                                                             ARCHIVEFILE ASMFILE
          31 +DATA/CS/CONTROLFILE/current.276.970601979                                                 CONTROLFILE ASMFILE
31 rows selected.

可以使用dbms_storage_map PL/SQL包中的過程來控制映射操作。例如，可以使用dbms_storage_map.map_object過程通過指定對(duì)象名，所有者與類型來對(duì)數(shù)據(jù)庫對(duì)象來構(gòu)建映射信息。在dbms_storage_map.map_object過程運(yùn)行之后，那么可以通過查詢map_object視圖來查詢映射信息

SQL> execute dbms_storage_map.map_object('T1','C##TEST','TABLE');
PL/SQL procedure successfully completed.
SQL> select io.object_name o_name, io.object_owner o_owner, io.object_type o_type,
  2  mf.file_name, me.elem_name, io.depth,
  3  (sum(io.cu_size * (io.num_cu - decode(io.parity_period, 0, 0,
  4  trunc(io.num_cu / io.parity_period)))) / 2) o_size
  5  from map_object io, v$map_element me, v$map_file mf
  6  where io.object_name = 'T1'
  7  and io.object_owner = 'C##TEST'
and io.object_type = 'TABLE'
  8    9  and me.elem_idx = io.elem_idx
 10  and mf.file_map_idx = io.file_map_idx
 11  group by io.elem_idx, io.file_map_idx, me.elem_name, mf.file_name, io.depth,
 12  io.object_name, io.object_owner, io.object_type
 13  order by io.depth;
O_NAME               O_OWNER              O_TYP FILE_NAME                                          ELEM_NAME                 DEPTH     O_SIZE
-------------------- -------------------- ----- -------------------------------------------------- -------------------- ---------- ----------
T1                   C##TEST              TABLE +DATA/CS/DATAFILE/users.275.970601909              +/dev/asmdisk04               0         64

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