Only ARCH Bgprocess may create archivelog?-阿里云开发者社区

我们在学习Oracle入门知识时都会介绍到ARCH归档进程，归档进程ARCH负责将在线重做日志归档，注意ARCH只会将日志文件中存在的重做内容复制到归档日志文件中，举例来说重做日志文件的大小是512MB，但当前写入的redo entry只占用10MB空间，此时由某些条件触发了日志切换，那么产生的归档文件的大小仍是10MB。一直以来存在着这样一种误解：归档操作只会由ARCH进程负责完成。实际上归档操作可能由多种进程完成，举例来说前台进程Fore ground process就可以完成归档操作，当在前台进程中执行alter system archive log current命令时实际执行归档操作的是前台进程(server process)，而非ARCH，这可能是大多数人料想之外的，口说无凭，我们具体验证一下:

[oracle@rh2 ~]$ ps -ef|grep LOCAL=YES|grep G10R2
oracle   20790 20789  0 19:17 ?        00:00:00 oracleG10R2 (DESCRIPTION=(LOCAL=YES)(ADDRESS=(PROTOCOL=beq)))

SQL> set linesize 200 pagesize 1400;
SQL> select le.leseq "Current log sequence No",
  2         100 * cp.cpodr_bno / le.lesiz "Percent Full",
  3         (cpodr_bno - 1) * 512  "bytes used exclude header",
  4         le.lesiz * 512 - cpodr_bno * 512 "Left space",
  5         le.lesiz  *512       "logfile size"
  6    from x$kcccp cp, x$kccle le
  7   where LE.leseq = CP.cpodr_seq
  8     and bitand(le.leflg, 24) = 8;

Current log sequence No Percent Full bytes used exclude header Left space logfile size
----------------------- ------------ ------------------------- ---------- ------------
                    720   62.0244141                  32518144   19910144     52428800

/* 通过以上脚本可以了解当前日志文件(current logfile)的使用情况，
    这里可以看到日志文件大小为50MB，已使用32MB                    */

[oracle@rh2 ~]$ strace -p 20972 -o archive.log
Process 20972 attached - interrupt to quit

SQL> alter system archive log current;
System altered.

[oracle@rh2 ~]$ cat archive.log |egrep "open|read|write"
read(8, "\1\2\0\0\6\0\0\0\0\0\3^\10!\200\0\0\0\0\0\0\30\352\341\0\0\0\0\0`\0\0"..., 2064) = 258
open("/s01/admin/G10R2/bdump/alert_G10R2.log", O_WRONLY|O_CREAT|O_APPEND, 0660) = 6
writev(6, [{"Mon May 30 19:31:23 2011\n", 25}, {"ALTER SYSTEM ARCHIVE LOG", 24}, {"\n", 1}], 3) = 50
open("/flashcard/oradata/G10R2/controlfile/1.ctl", O_RDWR|O_SYNC|O_DIRECT) = 12
pread(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\361\374\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\17\0\0\0\2324\0\0\377\377\1\4?^\0\0\0\6\0\0\0\0\0\0\0\0\0\2"..., 16384, 245760) = 16384
pread(12, "\25\302\0\0\21\0\0\0\2324\0\0\377\377\1\4\377\37\0\0\0\0\0\0\0\0\0\0Q\350\255,"..., 16384, 278528) = 16384
pread(12, "\25\302\0\0\26\0\0\0\2234\0\0\377\377\1\4\327\312\0\0\0\220\1\0\316\2\0\0\2\0\0\0"..., 16384, 360448) = 16384
pread(12, "\25\302\0\0\23\0\0\0\2174\0\0\377\377\1\4\372\202\0\0\17\0\0\0\265!\315\0\0\0/\234"..., 16384, 311296) = 16384
pwrite(12, "\25\302\0\0\22\0\0\0\2334\0\0\377\377\1\4B\35\0\0\0\0\0\0\0\0\0\0Q\350\255,"..., 16384, 294912) = 16384
pwrite(12, "\25\302\0\0\20\0\0\0\2334\0\0\377\377\1\4\240^\0\0\200\6\0\0\0\0\0\0\0\0\0\2"..., 16384, 262144) = 16384
pwrite(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\t\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\t\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\r\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\20\0\0\0\2354\0\0\377\377\1\4\241\177\0\0\200'\0\0\0\0\0\0\0\0\0\2"..., 16384, 262144) = 16384
pread(12, "\25\302\0\0\22\0\0\0\2354\0\0\377\377\1\4X\35\0\0\0\0\0\0\0\0\0\0Q\350\255,"..., 16384, 294912) = 16384
pread(12, "\25\302\0\0\26\0\0\0\2354\0\0\377\377\1\4\236W\0\0\0\220\1\0\321\2\0\0\1\0\0\0"..., 16384, 360448) = 16384
pread(12, "\25\302\0\0\36\0\0\0\2354\0\0\377\377\1\4\367\5\0\0\3\0\3\0\2\0\0\0\0\0/f"..., 16384, 491520) = 16384
open("/flashcard/oradata/G10R2/onlinelog/o1_mf_3_6v34jpmp_.log", O_RDONLY|O_DIRECT) = 13
open("/flashcard/oradata/G10R2/onlinelog/o1_mf_3_6v34jpmp_.log", O_RDWR|O_SYNC|O_DIRECT) = 13
open("/s01/flash_recovery_area/G10R2/onlinelog/o1_mf_3_6v34jpyn_.log", O_RDONLY|O_DIRECT) = 14
open("/s01/flash_recovery_area/G10R2/onlinelog/o1_mf_3_6v34jpyn_.log", O_RDWR|O_SYNC|O_DIRECT) = 14
pread(13, "\1\"\0\0\1\0\0\0\320\2\0\0\0\200Um\0\0\0\0\0\3 \n\22\235\205\254G10R"..., 512, 512) = 512
pread(14, "\1\"\0\0\1\0\0\0\320\2\0\0\0\200Um\0\0\0\0\0\3 \n\22\235\205\254G10R"..., 512, 512) = 512
open("/flashcard/oradata/G10R2/onlinelog/o1_mf_3_6v34jpmp_.log", O_RDONLY|O_DIRECT) = 13
open("/flashcard/oradata/G10R2/onlinelog/o1_mf_3_6v34jpmp_.log", O_RDWR|O_SYNC|O_DIRECT) = 13
open("/s01/flash_recovery_area/G10R2/onlinelog/o1_mf_3_6v34jpyn_.log", O_RDONLY|O_DIRECT) = 14
open("/s01/flash_recovery_area/G10R2/onlinelog/o1_mf_3_6v34jpyn_.log", O_RDWR|O_SYNC|O_DIRECT) = 14
pread(13, "\1\"\0\0\1\0\0\0\320\2\0\0\0\200Um\0\0\0\0\0\3 \n\22\235\205\254G10R"..., 512, 512) = 512
pread(14, "\1\"\0\0\1\0\0\0\320\2\0\0\0\200Um\0\0\0\0\0\3 \n\22\235\205\254G10R"..., 512, 512) = 512
pread(12, "\25\302\0\0\24\0\0\0\2354\0\0\377\377\1\4\341\202\0\0\17\0\0\0\265!\315\0\0\0/\234"..., 16384, 327680) = 16384
pread(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\r\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\20\0\0\0\2354\0\0\377\377\1\4\241\177\0\0\200'\0\0\0\0\0\0\0\0\0\2"..., 16384, 262144) = 16384
pread(12, "\25\302\0\0\22\0\0\0\2354\0\0\377\377\1\4X\35\0\0\0\0\0\0\0\0\0\0Q\350\255,"..., 16384, 294912) = 16384
pread(12, "\25\302\0\0D\1\0\0\2234\0\0\377\377\1\4L\250\0\0\0\0\0\0\0\0\0\0008\251\332,"..., 16384, 5308416) = 16384
pread(12, "\25\302\0\0A\1\0\0\2234\0\0\377\377\1\4\3715\0\0\0\236<\216\5\0\0\0\0\300[\310"..., 16384, 5259264) = 16384
pwrite(12, "\25\302\0\0C\1\0\0\2364\0\0\377\377\1\4\210\232\0\0\0000\360\1\0\0\0\0\v\252\332,"..., 16384, 5292032) = 16384
pwrite(12, "\25\302\0\0\21\0\0\0\2364\0\0\377\377\1\4[\35\0\0\0\0\0\0\0\0\0\0Q\350\255,"..., 16384, 278528) = 16384
pwrite(12, "\25\302\0\0\17\0\0\0\2364\0\0\377\377\1\4?\177\0\0\0'\0\0\0\0\0\0\0\0\0\2"..., 16384, 245760) = 16384
pwrite(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\r\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\r\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
open("/s01/flash_recovery_area/G10R2/archivelog/2011_05_30/o1_mf_1_720_6y700ch9_.arc", O_RDWR|O_CREAT|O_EXCL|O_SYNC, 0660) = 15
open("/s01/flash_recovery_area/G10R2/archivelog/2011_05_30/o1_mf_1_720_6y700ch9_.arc", O_RDWR|O_SYNC|O_DIRECT) = 15
write(15, "\0\"\0\0\0\0\300\377\0\0\0\0\0\0\0\0~\240\0\0\0\2\0\0\30\370\0\0}|{z"..., 512) = 512
open("/s01/flash_recovery_area/G10R2/archivelog/2011_05_30/o1_mf_1_720_6y700ch9_.arc", O_RDONLY|O_DIRECT) = 15
open("/s01/flash_recovery_area/G10R2/archivelog/2011_05_30/o1_mf_1_720_6y700ch9_.arc", O_RDWR|O_DIRECT) = 15
pread(13, "\1\"\0\0\1\0\0\0\320\2\0\0\0\200Um\0\0\0\0\0\3 \n\22\235\205\254G10R"..., 1048576, 512) = 1048576
pwrite(15, "\1\"\0\0\1\0\0\0\320\2\0\0\0\200tm\0\0\0\0\0\3 \n\22\235\205\254G10R"..., 1048576, 512) = 1048576
pread(13, "\1\"\0\0\1\10\0\0\320\2\0\0\0\200\271\242:22:48:01\5VALID\1"..., 1048576, 1049088) = 1048576
pwrite(15, "\1\"\0\0\1\10\0\0\320\2\0\0\0\200\271\242:22:48:01\5VALID\1"..., 1048576, 1049088) = 1048576
pread(13, "\1\"\0\0\1\20\0\0\320\2\0\0\0\200\220\271\n\0232011-05-12:22:"..., 1048576, 2097664) = 1048576
pwrite(15, "\1\"\0\0\1\20\0\0\320\2\0\0\0\200\220\271\n\0232011-05-12:22:"..., 1048576, 2097664) = 1048576
pread(13, "\1\"\0\0\1\30\0\0\320\2\0\0\364\201\261/\21\0232011-05-12:22:"..., 1048576, 3146240) = 1048576
pwrite(15, "\1\"\0\0\1\30\0\0\320\2\0\0\364\201\261/\21\0232011-05-12:22:"..., 1048576, 3146240) = 1048576
pread(13, "\1\"\0\0\1 \0\0\320\2\0\0\0\200\31~:22:54:21\5VALID\1"..., 1048576, 4194816) = 1048576
pwrite(15, "\1\"\0\0\1 \0\0\320\2\0\0\0\200\31~:22:54:21\5VALID\1"..., 1048576, 4194816) = 1048576
pread(13, "\1\"\0\0\1(\0\0\320\2\0\0\0\200\320\210\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 5243392) = 1048576
pwrite(15, "\1\"\0\0\1(\0\0\320\2\0\0\0\200\320\210\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 5243392) = 1048576
pread(13, "\1\"\0\0\0010\0\0\320\2\0\0\374\200\265$\5\f\27<\10\7xo\5\f\27<\10\02320"..., 1048576, 6291968) = 1048576
pwrite(15, "\1\"\0\0\0010\0\0\320\2\0\0\374\200\265$\5\f\27<\10\7xo\5\f\27<\10\02320"..., 1048576, 6291968) = 1048576
pread(13, "\1\"\0\0\0018\0\0\320\2\0\0\0\200W&796508\377\5\304\2\6\2\t\377\tP"..., 1048576, 7340544) = 1048576
pwrite(15, "\1\"\0\0\0018\0\0\320\2\0\0\0\200W&796508\377\5\304\2\6\2\t\377\tP"..., 1048576, 7340544) = 1048576
pread(13, "\1\"\0\0\1@\0\0\320\2\0\0\0\200*2SYS\7D807355\377\5\304\2\7"..., 1048576, 8389120) = 1048576
pwrite(15, "\1\"\0\0\1@\0\0\320\2\0\0\0\200*2SYS\7D807355\377\5\304\2\7"..., 1048576, 8389120) = 1048576
pread(13, "\1\"\0\0\1H\0\0\320\2\0\0\0\200~\5\tPROCEDURE\7xo\5\f\30"..., 1048576, 9437696) = 1048576
pwrite(15, "\1\"\0\0\1H\0\0\320\2\0\0\0\200~\5\tPROCEDURE\7xo\5\f\30"..., 1048576, 9437696) = 1048576
pread(13, "\1\"\0\0\1P\0\0\320\2\0\0\0\200ll\5\f\30\10'\0232011-05-12"..., 1048576, 10486272) = 1048576
pwrite(15, "\1\"\0\0\1P\0\0\320\2\0\0\0\200ll\5\f\30\10'\0232011-05-12"..., 1048576, 10486272) = 1048576
pread(13, "\1\"\0\0\1X\0\0\320\2\0\0\0\200\320\370\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 11534848) = 1048576
pwrite(15, "\1\"\0\0\1X\0\0\320\2\0\0\0\200\320\370\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 11534848) = 1048576
pread(13, "\1\"\0\0\1`\0\0\320\2\0\0\0\200\27\216 \377\tPROCEDURE\7xo\5"..., 1048576, 12583424) = 1048576
pwrite(15, "\1\"\0\0\1`\0\0\320\2\0\0\0\200\27\216 \377\tPROCEDURE\7xo\5"..., 1048576, 12583424) = 1048576
pread(13, "\1\"\0\0\1h\0\0\320\2\0\0008\201fj\1N\1N,\0\r\3SYS\7D860"..., 1048576, 13632000) = 1048576
pwrite(15, "\1\"\0\0\1h\0\0\320\2\0\0008\201fj\1N\1N,\0\r\3SYS\7D860"..., 1048576, 13632000) = 1048576
pread(13, "\1\"\0\0\1p\0\0\320\2\0\0\0\200\25%\7xo\5\f\30\20:\0232011-05"..., 1048576, 14680576) = 1048576
pwrite(15, "\1\"\0\0\1p\0\0\320\2\0\0\0\200\25%\7xo\5\f\30\20:\0232011-05"..., 1048576, 14680576) = 1048576
pread(13, "\1\"\0\0\1x\0\0\320\2\0\0\0\200G\36\7xo\5\f\30\23\6\7xo\5\f\30\23\6"..., 1048576, 15729152) = 1048576
pwrite(15, "\1\"\0\0\1x\0\0\320\2\0\0\0\200G\36\7xo\5\f\30\23\6\7xo\5\f\30\23\6"..., 1048576, 15729152) = 1048576
pread(13, "\1\"\0\0\1\200\0\0\320\2\0\0004\200\"\34311-05-12:23:20:1"..., 1048576, 16777728) = 1048576
pwrite(15, "\1\"\0\0\1\200\0\0\320\2\0\0004\200\"\34311-05-12:23:20:1"..., 1048576, 16777728) = 1048576
pread(13, "\1\"\0\0\1\210\0\0\320\2\0\0\0\200\320(\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 17826304) = 1048576
pwrite(15, "\1\"\0\0\1\210\0\0\320\2\0\0\0\200\320(\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 17826304) = 1048576
pread(13, "\1\"\0\0\1\220\0\0\320\2\0\0\0\200\343\367\377\tPROCEDURE\7xo\5\f"..., 1048576, 18874880) = 1048576
pwrite(15, "\1\"\0\0\1\220\0\0\320\2\0\0\0\200\343\367\377\tPROCEDURE\7xo\5\f"..., 1048576, 18874880) = 1048576
pread(13, "\1\"\0\0\1\230\0\0\320\2\0\0\350\201\200\263\33\32\0232011-05-12:23"..., 1048576, 19923456) = 1048576
pwrite(15, "\1\"\0\0\1\230\0\0\320\2\0\0\350\201\200\263\33\32\0232011-05-12:23"..., 1048576, 19923456) = 1048576
pread(13, "\1\"\0\0\1\240\0\0\320\2\0\0\34\201\36\326-12:23:28:30\5VAL"..., 1048576, 20972032) = 1048576
pwrite(15, "\1\"\0\0\1\240\0\0\320\2\0\0\34\201\36\326-12:23:28:30\5VAL"..., 1048576, 20972032) = 1048576
pread(13, "\1\"\0\0\1\250\0\0\320\2\0\0\0\200P\331VALID\1N\1N\1N,\0\r\3S"..., 1048576, 22020608) = 1048576
pwrite(15, "\1\"\0\0\1\250\0\0\320\2\0\0\0\200P\331VALID\1N\1N\1N,\0\r\3S"..., 1048576, 22020608) = 1048576
pread(13, "\1\"\0\0\1\260\0\0\320\2\0\0\0\200\342X\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 23069184) = 1048576
pwrite(15, "\1\"\0\0\1\260\0\0\320\2\0\0\0\200\342X\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1048576, 23069184) = 1048576
pread(13, "\1\"\0\0\1\270\0\0\320\2\0\0\0\200k\251,\0\r\3SYS\7D968280\377"..., 1048576, 24117760) = 1048576
pwrite(15, "\1\"\0\0\1\270\0\0\320\2\0\0\0\200k\251,\0\r\3SYS\7D968280\377"..., 1048576, 24117760) = 1048576
pread(13, "\1\"\0\0\1\300\0\0\320\2\0\0\310\200Ix:37:19\5VALID\1N\1N"..., 1048576, 25166336) = 1048576
pwrite(15, "\1\"\0\0\1\300\0\0\320\2\0\0\310\200Ix:37:19\5VALID\1N\1N"..., 1048576, 25166336) = 1048576
pread(13, "\1\"\0\0\1\310\0\0\320\2\0\0\0\200\34*#\7\377\tPROCEDURE\7xo"..., 1048576, 26214912) = 1048576
pwrite(15, "\1\"\0\0\1\310\0\0\320\2\0\0\0\200\34*#\7\377\tPROCEDURE\7xo"..., 1048576, 26214912) = 1048576
pread(13, "\1\"\0\0\1\320\0\0\320\2\0\0\0\200\343\336A\377\tPROCEDURE\7xo\5"..., 1048576, 27263488) = 1048576
pwrite(15, "\1\"\0\0\1\320\0\0\320\2\0\0\0\200\343\336A\377\tPROCEDURE\7xo\5"..., 1048576, 27263488) = 1048576
pread(13, "\1\"\0\0\1\330\0\0\320\2\0\0P\200\367{/\377\tPROCEDURE\7xo\5"..., 1048576, 28312064) = 1048576
pwrite(15, "\1\"\0\0\1\330\0\0\320\2\0\0P\200\367{/\377\tPROCEDURE\7xo\5"..., 1048576, 28312064) = 1048576
pread(13, "\1\"\0\0\1\340\0\0\320\2\0\0\0\200\315_-05-12:23:46:08\5"..., 1048576, 29360640) = 1048576
pwrite(15, "\1\"\0\0\1\340\0\0\320\2\0\0\0\200\315_-05-12:23:46:08\5"..., 1048576, 29360640) = 1048576
pread(13, "\1\"\0\0\1\350\0\0\320\2\0\0\0\200\263Xo\5\f\0302\31\7xo\5\f\0302\31\0232"..., 1048576, 30409216) = 1048576
pwrite(15, "\1\"\0\0\1\350\0\0\320\2\0\0\0\200\263Xo\5\f\0302\31\7xo\5\f\0302\31\0232"..., 1048576, 30409216) = 1048576
pread(13, "\1\"\0\0\1\360\0\0\320\2\0\0\0\200\213K\5VALID\1N\1N\1N,\0\r\3"..., 1048576, 31457792) = 1048576
pwrite(15, "\1\"\0\0\1\360\0\0\320\2\0\0\0\200\213K\5VALID\1N\1N\1N,\0\r\3"..., 1048576, 31457792) = 1048576
pread(13, "\1\"\0\0\1\370\0\0\320\2\0\0\300\200\333N\24\0\t\0T\0\210\22\"\0\0\0\t\0\t\0"..., 12288, 32506368) = 12288
pwrite(15, "\1\"\0\0\1\370\0\0\320\2\0\0\300\200\333N\24\0\t\0T\0\210\22\"\0\0\0\t\0\t\0"..., 12288, 32506368) = 12288
open("/s01/flash_recovery_area/G10R2/archivelog/2011_05_30/o1_mf_1_720_6y700ch9_.arc", O_RDWR|O_DIRECT) = 16
write(16, "\0\"\0\0\0\0\300\377\0\0\0\0\0\0\0\0~\240\0\0\0\2\0\0\30\370\0\0}|{z"..., 512) = 512
open("/s01/flash_recovery_area/G10R2/archivelog/2011_05_30/o1_mf_1_720_6y700ch9_.arc", O_RDWR|O_DIRECT) = 16
write(16, "\0\"\0\0\0\0\300\377\0\0\0\0\0\0\0\0~\240\0\0\0\2\0\0\30\370\0\0}|{z"..., 512) = 512
pread(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\4\r\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\17\0\0\0\2364\0\0\377\377\1\4?\177\0\0\0'\0\0\0\0\0\0\0\0\0\2"..., 16384, 245760) = 16384
pread(12, "\25\302\0\0\21\0\0\0\2364\0\0\377\377\1\4[\35\0\0\0\0\0\0\0\0\0\0Q\350\255,"..., 16384, 278528) = 16384
pread(12, "\25\302\0\0\26\0\0\0\2354\0\0\377\377\1\4\236W\0\0\0\220\1\0\321\2\0\0\1\0\0\0"..., 16384, 360448) = 16384
pread(12, "\25\302\0\0\313\0\0\0\2234\0\0\377\377\1\4\2\245\0\0005\251\332,D\"\315\0\0\0\0\0"..., 16384, 3325952) = 16384
pread(12, "\25\302\0\0(\1\0\0d4\0\0\377\377\1\4\6*\0\0\33\0\4\0\333\7\0\0\0\0\0\0"..., 16384, 4849664) = 16384
pread(12, "\25\302\0\0A\1\0\0\2234\0\0\377\377\1\4\3715\0\0\0\236<\216\5\0\0\0\0\300[\310"..., 16384, 5259264) = 16384
pread(12, "\25\302\0\0\313\0\0\0\2234\0\0\377\377\1\4\2\245\0\0005\251\332,D\"\315\0\0\0\0\0"..., 16384, 3325952) = 16384
pwrite(12, "\25\302\0\0B\1\0\0\2374\0\0\377\377\1\4\3725\0\0\0\236<\216\5\0\0\0\0\300[\310"..., 16384, 5275648) = 16384
pread(12, "\25\302\0\0C\1\0\0\2364\0\0\377\377\1\4\210\232\0\0\0000\360\1\0\0\0\0\v\252\332,"..., 16384, 5292032) = 16384
pread(12, "\25\302\0\0B\1\0\0\2374\0\0\377\377\1\4\3725\0\0\0\236<\216\5\0\0\0\0\300[\310"..., 16384, 5275648) = 16384
pwrite(12, "\25\302\0\0D\1\0\0\2374\0\0\377\377\1\4\177\253\0\0\0\0\0\0\0\0\0\0\v\252\332,"..., 16384, 5308416) = 16384
pread(12, "\25\302\0\0\313\0\0\0\2234\0\0\377\377\1\4\2\245\0\0005\251\332,D\"\315\0\0\0\0\0"..., 16384, 3325952) = 16384
pwrite(12, "\25\302\0\0B\1\0\0\2374\0\0\377\377\1\4\353{\0\0\0\316,\220\5\0\0\0\0\300[\310"..., 16384, 5275648) = 16384
pread(12, "\25\302\0\0\26\0\0\0\2354\0\0\377\377\1\4\236W\0\0\0\220\1\0\321\2\0\0\1\0\0\0"..., 16384, 360448) = 16384
pwrite(12, "\25\302\0\0\25\0\0\0\2374\0\0\377\377\1\4\236W\0\0\0\220\1\0\321\2\0\0\1\0\0\0"..., 16384, 344064) = 16384
pwrite(12, "\25\302\0\0\314\0\0\0\2374\0\0\377\377\1\4\231@\0\0005\251\332,D\"\315\0\0\0\0\0"..., 16384, 3342336) = 16384
pwrite(12, "\25\302\0\0\22\0\0\0\2374\0\0\377\377\1\4\323\35\0\0\0\0\0\0\0\0\0\0Q\350\255,"..., 16384, 294912) = 16384
pwrite(12, "\25\302\0\0\20\0\0\0\2374\0\0\377\377\1\4\261\375\0\0\200%\0\0\0\0\0\0\0\0\0\2"..., 16384, 262144) = 16384
pwrite(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\0043\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
pread(12, "\25\302\0\0\1\0\0\0\0\0\0\0\0\0\1\0043\377\0\0\0\0\0\0\0\3 \n\22\235\205\254"..., 16384, 16384) = 16384
write(11, "\0\313\0\0\6\0\0\0\0\0\10\6\0\315\"\315\0\0\0\0\0\1\0\0\0\0\0\0\0\0\0\0"..., 203) = 203

在以上system call trace中可以看到前台进程首先读取并更新了控制文件(controlfile/1.ctl)，之后读取了在线日志文件的头部(read o1_mf_3_6v34jpmp_.log=512bytes),接着以相关属性创建了归档日志文件(o1_mf_1_720_6y700ch9_.arc，注意这里使用了O_CREAT、O_EXCL、O_SYNC、0660属性)并得到该打开文件描述符15，接着以每次buffer为1048576字节来读取在线日志并写入归档日志pread(onlinelog)->pwrite(archivelog)，直到在线日志中的redo记录被写完。这里的buffer大小1048576实际上受到隐藏参数_log_archive_buffer_size(Size of each archival buffer in log file blocks)的影响，该参数指定了归档缓冲的大小，其单位为日志文件块(log file block)，日志文件块大小在不同平台上各有差异，具体可以参考这里。目前主流的UNIX平台上日志文件标准块大小为512 bytes，而_log_archive_buffer_size的默认值一般为2048，所以得出了这里的(2048*512)=1048576=1MB buffer大小。需要注意的是与"alter system archive log current"命令不同，"switch logfile"不会引起前台进程去执行归档操作，归档操作仍将由ARCH进程完成。我们可以很方便的通过查询v$archived_log视图来了解具体完成某个日志文件归档操作的是何种进程，这得益于其creator列:

SQL> select distinct creator  from v$archived_log;

CREATOR
-------
RMAN
FGRD
ARCH


CREATOR 	VARCHAR2(7) 	Creator of the archivelog:

    ARCH - Archiver process
    FGRD - Foreground process
    RMAN - Recovery Manager
    SRMN - RMAN at standby
    LGWR - Logwriter process

以上可以看到可能创建归档日志的进程不仅仅局限于FGRD与ARCH，RMAN(注意实际上并非直接由rman进程完成)在执行热备操作时也可能掺合进来归档一把，此外在DataGuard环境中LGWR也会参与归档操作。 V$archived_log视图中另外一个有趣的字段是REGISTRAR，一般来说在非DataGuard环境中CREATOR总是等于REGISTRAR，而在DataGuard环境中REGISTRAR常是RFS(remote file server process (RFS) on the standby system where the RFS process writes the redo data to either archived redo log files or standby redo log files)后台进程，而实际的CREATOR则往往仍是ARCH或LGWR。

LGWR - Logwriter process

本文转自maclean_007 51CTO博客，原文链接:
http://blog.51cto.com/maclean/1277808

Only ARCH Bgprocess may create archivelog?

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Only ARCH Bgprocess may create archivelog?

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