Oracle内存结构（之三）

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【深入解析--eygle】学习笔记

1.2.3 PGA的管理：

sys@felix SQL>show parameter area_size NAME                                 TYPE                   VALUE------------------------------------ ----------------------------------------------------bitmap_merge_area_size               integer                1048576create_bitmap_area_size              integer                8388608hash_area_size                       integer                131072sort_area_size                       integer                65536workarea_size_policy                 string                 AUTO

自动化SQL执行内存管理（Automated SQL Execution Memory Management），也称为自动PGA管理，使用这个新特性，Oracle可以在一个总体PGA使用限制下自动管理和调整SQL内存区，从而大大简化了DBA的工作，同时也ᨀ高了数据库的性能。

为实现自动的PGA管理，Oracle引入了几个新的初始化参数：

（1）PGA_AGGREGATE_TARGET 此参数用来指定所有session 总计可以使用最大PGA内存。这个参数可以被动态的更改,取值范围从10M ～（4096G-1 ）bytes。

（2）WORKAREA_SIZE_POLICY此参数用于开关PGA内存自动管理功能，该参数有两个选项：AUTO 和 MANUAL，当设置为AUTO时，数据库使用自动PGA管理功能，当设置为MANUAL时，则仍然使用之前手工管理的方式。

缺省的，WORKAREA_SIZE_POLICY参数被设置为AUTO。

sys@felix SQL>show parameterWORKAREA_SIZE_POLIC NAME                                 TYPE                   VALUE---------------------------------------------------------- --------workarea_size_policy                 string                 AUTO

此外需要注意的是，在不同版本中，自动PGA管理的范畴不同：

（1）在Oracle9i中，PGA_AGGREGATE_TARGET参数仅对专用服务器模式下（DedicatedServer）的专属连接有效，但是对共享服务器（Shared Server）连接无效

（2）从Oracle10g开始PGA_AGGREGATE_TARGET对专用服务器连接和共享服务器连接同时生效。

1.2.4 参数的设置与内存分配

工作区性能期望实现如下目标：

workarea execution - optimal >= 90%

workarea execution - multipass = 0%

生产系统的PGA性能指标脚本:

SELECT NAME,      VALUE,       100 *      (VALUE / DECODE((SELECT SUM(VALUE)                         FROM v$sysstat                        WHERE NAME LIKE'workarea executions%'),                       0,                       NULL,                       (SELECT SUM(VALUE)                          FROM v$sysstat                         WHERE NAME LIKE'workarea executions%'))) pct  FROMv$sysstat WHERE NAMELIKE 'workarea executions%';

<strong>sys@felix SQL>select description,dest fromx$messages where description like 'SQL Memory%'; DESCRIPTION                                        DEST-------------------------------------------------- ----------SQL Memory Management Calculation                  CKPT 15:26:04 sys@felix SQL></strong>

sys@felix SQL>select * from v$pgastat;NAME                                          VALUE UNIT---------------------------------------- ---------- ------------------------aggregate PGA target parameter            146800640 bytesaggregate PGA auto target                  22099968 bytesglobal memory bound                        29360128 bytestotal PGA inuse                           122360832 bytestotal PGA allocated                       144107520 bytesmaximum PGA allocated                     163160064 bytestotal freeable PGA memory                  11141120 bytesprocess count                                    32max processes count                              36PGA memory freed back to OS               374669312 bytestotal PGA used for auto workareas                 0 bytesmaximum PGA used for auto workareas         6313984 bytestotal PGA used for manual workareas               0 bytesmaximum PGA used for manual workareas             0 bytesover allocation count                             0bytes processed                           232915968 bytesextra bytes read/written                          0 bytescache hit percentage                            100 percentrecompute count (total)                        600419 rows selected.

1.2.6 PGA调整建议

伴随自动PGA调整功能的引入，Oracle同时引入相应的动态性能视图用于优化建议，PGA的优化建议通过v$pga_target_advice 和 v$pga_target_advice_histogra提供。v$pga_target_advice视图通过对不同PGA设置进行评估，给出在不同设置下的PGA命中率和OverAlloc等信息。

15:32:23 sys@felix SQL>select PGA_TARGET_FOR_ESTIMATE/1024/1024 PGAMB, PGA_TARGET_FACTOR, 15:37:08   2  ESTD_PGA_CACHE_HIT_PERCENTAGE, ESTD_OVERALLOC_COUNT15:37:08   3  from v$pga_target_advice;     PGAMB PGA_TARGET_FACTOR ESTD_PGA_CACHE_HIT_PERCENTAGE ESTD_OVERALLOC_COUNT---------- ----------------- ----------------------------- --------------------      17.5              .125                            85                    4        35               .25                            85                    4        70                .5                            85                    4       105               .75                            85                    4       140                 1                           100                    0       168               1.2                           100                    0       196               1.4                           100                    0       224               1.6                           100                    0       252               1.8                           100                    0       280                 2                           100                    0       420                 3                           100                    0       560                 4                           100                    0       840                 6                           100                    0      1120                 8                           100                    0

v$pga_target_advice_histogram 视图可以通过对不同工作区大小的采样评估ᨀ供统计信息

供分析使用。其中几个重要字段有：

（1）LOW_OPTIMAL_SIZE-Histogram评估区间内Optimal下限 (bytes)

（2）HIGH_OPTIMAL_SIZE-Histogram评估区间内Optimal上限 (bytes)

（3）ESTD_OPTIMAL_EXECUTIONS-Histogram评估区间内估计optimal执行次数

（4）ESTD_ONEPASS_EXECUTIONS-Histogram评估区间内估计onepass执行次数

（5）ESTD_MULTIPASSES_EXECUTIONS-Histogram评估区间内估计multipass执行次数

（6）ESTD_TOTAL_EXECUTIONS-Histogram评估区间内估计执行总次数

SELECT pga_target_factor factor,       low_optimal_size / 1024 low,       ROUND(high_optimal_size / 1024) high,       estd_optimal_executions estd_opt,       estd_onepass_executions estd_op,       estd_multipasses_executions estd_mp,       estd_total_executions estd_exec  FROM v$pga_target_advice_histogram WHERE pga_target_factor = 0.25   AND estd_total_executions > 0;

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<span style="font-family: Arial, Helvetica, sans-serif;"></span>

<span style="font-family: Arial, Helvetica, sans-serif;"> heap name="pga heap"  desc=0xbaf3ca0   --注意这里</span></strong></span>

 extentsz=0x20c0 alt=216 het=32767 rec=0 flg=3 opc=2 parent=(nil)owner=(nil) nex=(nil) xsz=0xfff0 heap=(nil) fl2=0x60,nex=(nil), dsxvers=1, dsxflg=0x0 dsx firstext=0xf7fa7720EXTENT 0 addr=0x7fadf7c72010  Chunk     7fadf7c72020 sz=    65504   free      "               "EXTENT 1 addr=0x7fadf7d00010  Chunk     7fadf7d00020 sz=    28920   perm      "perm           "  alo=9384  Chunk     7fadf7d07118 sz=     7656   free      "               "  Chunk     7fadf7d08f00 sz=     4224   freeable  "diag pga       " ds=0x7fadf82157e0  Chunk     7fadf7d09f80 sz=     4224   freeable  "diag pga       " ds=0x7fadf82157e0/heap                                                                                                                              Chunk     7fadf7fd28d0 sz=     7608   perm      "perm           "  alo=7608  Chunk     7fadf7fd4688 sz=       40   free      "               "  Chunk     7fadf7fd46b0 sz=       80   freeable  "dbgdInitEventGr"  Chunk     7fadf7fd4700 sz=      184   freeable  "sdbgrf: iosb   "  Chunk     7fadf7fd47b8 sz=       80   freeable  "skgfzctx       "  Chunk     7fadf7fd4808 sz=      376   freeable  "PLS cca hpdesc"EXTENT 18 addr=0x7fadf7fcd860  Chunk     7fadf7fcd870 sz=    20512   perm      "perm           "  alo=20512EXTENT 19 addr=0x7fadf7fc9958  Chunk     7fadf7fc9968 sz=    16072   perm      "perm           "  alo=16072EXTENT 20 addr=0x7fadf7fc7868  Chunk     7fadf7fc7878 sz=     3240   perm      "perm           "  alo=3240  Chunk     7fadf7fc8520 sz=     3184   perm      "perm           "  alo=3184  Chunk     7fadf7fc9190 sz=     1088   perm      "perm           "  alo=1088  Chunk     7fadf7fc95d0 sz=      168   perm      "perm           "  alo=168  Chunk     7fadf7fc9678 sz=       48   free      "               "  Chunk     7fadf7fc96a8 sz=       72   freeable  "koh-kghu callh"  Chunk     7fadf7fc96f0 sz=      568   freeable  "joxp heap      "EXTENT 21 addr=0x7fadf7fc5778  Chunk     7fadf7fc5788 sz=     4848   perm      "perm           "  alo=4848  Chunk     7fadf7fc6a78 sz=      440   freeable  "krbabrPgaRespMs"  Chunk     7fadf7fc6c30 sz=       56   freeable  "krbabrPgaReqCtx"  Chunk     7fadf7fc6c68 sz=      424   freeable  "krbabrPgaReqMsg"  Chunk     7fadf7fc6e10 sz=     2600   freeable  "kjztprq struct"EXTENT 22 addr=0x7fadf7fc3688  Chunk     7fadf7fc3698 sz=     7720   perm      "perm           "  alo=7720  Chunk     7fadf7fc54c0 sz=      160   freeable  "regheapd_kdlwpg"  Chunk     7fadf7fc5560 sz=       88   freeable  "KCFIS GCTX     "  Chunk     7fadf7fc55b8 sz=      400   freeable  "krbabrPgaStbyRe"EXTENT 23 addr=0x7fadf7fb5e28  Chunk     7fadf7fb5e38 sz=    55328   perm      "perm           "  alo=55328EXTENT 24 addr=0x7fadf7fb3d38  Chunk     7fadf7fb3d48 sz=     4888   perm      "perm           "  alo=4888  Chunk     7fadf7fb5060 sz=     2992   recreate  "KSFQ heap      " latch=(nil)

进一步的，可以将某个具体的数据存储结构转储出来（DS），如以上的ds dcd00c0其空间使用的大小为 sz= 14036，首先对空间地址进行一下转换：

select to_number('baf3ca0','xxxxxxxxxx') from dual15:50:33 sys@felix SQL>/TO_NUMBER('BAF3CA0','XXXXXXXXXX')---------------------------------                        19603369615:50:33 sys@felix SQL>

使用如下命令转储固定地址空间的内容：

alter session set events'immediate trace name heapdump_addr level 1, addr n';

以上计算的地址空间可以通过如下命令转储：

SQL> ALTER SESSIONSET EVENTS 'immediate trace name heapdump_addr level 1, addr 196033696';

Session altered.

获取转储文件的脚本：

SELECT a.VALUE || b.symbol || c.instance_name || '_ora_' || d.spid ||       '.trc' trace_file  FROM (SELECT VALUE FROM v$parameter WHERE NAME = 'user_dump_dest') a,       (SELECT SUBSTR(VALUE, -6, 1) symbol          FROM v$parameter         WHERE NAME = 'user_dump_dest') b,       (SELECT instance_name FROM v$instance) c,       (SELECT spid          FROM v$session s, v$process p, v$mystat m         WHERE s.paddr = p.addr           AND s.SID = m.SID           AND m.statistic# = 0) d;

检查这个进程转储文件，可以发现如下Heap地址信息及空间分配：

[oracle@felix ~]$grep heap  /u01/app/oracle/diag/rdbms/felix/felix/trace/felix_ora_6443.trc<strong><span style="color:#ff0000;">HEAP DUMP heap name="pga heap"  desc=0xbaf3ca0</span></strong> parent=(nil) owner=(nil) nex=(nil) xsz=0xfff0 heap=(nil)  Chunk     7fadf7fc96f0 sz=      568    freeable  "joxp heap      "  Chunk     7fadf7fc54c0 sz=      160    freeable  "regheapd_kdlwpg"  Chunk     7fadf7fb5060 sz=     2992    recreate  "KSFQ heap      "  latch=(nil)  Chunk     7fadf7fb5c10 sz=      160    freeable  "KSFQ heap descr"  Chunk     7fadf7fb0790 sz=      232    freeable  "iovecheapd_kdlw"  Chunk     7fadf7fb0878 sz=      304    freeable  "bcheapd_kdlwpga"  Chunk     7fadf7fb09a8 sz=      208    freeable  "sioheapd_kdlwpg"  Chunk     7fadf7fb0ad8 sz=      160    freeable  "KSZ pga subheap"Total heap size    =   499952<strong><span style="color:#ff0000;">HEAP DUMP heap name="top call heap"  desc=0xbaf94e0</span></strong> parent=(nil) owner=(nil) nex=(nil) xsz=0xfff8 heap=(nil)  Chunk     7fadf7ccb7d8 sz=     1032    recreate  "callheap       "  latch=(nil)  Chunk     7fadf7cceb78 sz=     4224    freeable  "callheap       "  ds=0xbaf85c0  Chunk     7fadf7ccfbf8 sz=     1032    recreate  "callheap       "  latch=(nil)Total heap size    =   524096

<strong><span style="color:#ff0000;">HEAP DUMP heap name="top uga heap"  desc=0xbaf9700</span></strong> parent=(nil) owner=(nil) nex=(nil) xsz=0xfff8 heap=(nil)  Chunk     7fadf7c62018 sz=    65512    freeable  "session heap   "  ds=0x7fadf7cd5be0  Chunk     7fadf7d10018 sz=    65512    freeable  "session heap   "  ds=0x7fadf7cd5be0  Chunk     7fadf7cf0018 sz=    65512    freeable  "session heap   "  ds=0x7fadf7cd5be0  Chunk     7fadf7ce0068 sz=    65432    recreate  "session heap   "  latch=(nil)Total heap size    =   262048<strong><span style="color:#ff0000;">HEAP DUMP heap name="pga heap"  desc=0xbaf3ca0</span></strong> parent=(nil) owner=(nil) nex=(nil) xsz=0x1fff0 heap=(nil)  Chunk     7fadf7fc96f0 sz=      568    freeable  "joxp heap      "  Chunk     7fadf7fc54c0 sz=      160    freeable  "regheapd_kdlwpg"  Chunk     7fadf7fb5060 sz=     2992    recreate  "KSFQ heap      "  latch=(nil)  Chunk     7fadf7fb5c10 sz=      160    freeable  "KSFQ heap descr"  Chunk     7fadf7fb0790 sz=      232    freeable  "iovecheapd_kdlw"  Chunk     7fadf7fb0878 sz=      304    freeable  "bcheapd_kdlwpga"  Chunk     7fadf7fb09a8 sz=      208    freeable  "sioheapd_kdlwpg"  Chunk     7fadf7fb0ad8 sz=      160    freeable  "KSZ pga subheap"Total heap size    =   827504

由上面红色字体可见，在自动管理模式下，PGA,CGA,UGA都是独立分配的。

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