Back in November 2008, I’ve asked question how to monitor VM cache performance (cache hit ratio) under Linux on Kevin Closson’s blog. Now I’ve just found utility that allows to show pretty nicely what *is* in VM cache. The utility is called “fincore”, it is written in Python and has some strange Python/perl dependecies, but it works:
[oracle@xeno test]$ fincore -justsummarize *.dbf page size: 4096 bytes 0 pages, 0.0 bytes in core for 10 files; 0.00 pages, 0.0 bytes per file. [oracle@xeno test]$ echo $ORACLE_SID oceperf [oracle@xeno test]$ sqlplus "/ as sysdba" SQL*Plus: Release 11.1.0.6.0 - Production on Tue Mar 17 10:35:01 2009 Copyright (c) 1982, 2007, Oracle. All rights reserved. Connected to an idle instance. SQL> startup; ORACLE instance started. Total System Global Area 535662592 bytes Fixed Size 1301112 bytes Variable Size 348128648 bytes Database Buffers 180355072 bytes Redo Buffers 5877760 bytes Database mounted. Database opened. SQL> show parameter filesystem NAME TYPE VALUE ------------------------------------ ----------- ------------------------------ filesystemio_options string none SQL>
So let’s verify again (11g on Linux uses O_DIRECT IO by default).
[oracle@xeno test]$ fincore -justsummarize *.dbf page size: 4096 bytes 0 pages, 0.0 bytes in core for 10 files; 0.00 pages, 0.0 bytes per file. [oracle@xeno test]$
Use those DBF files with VM cache (trick):
[oracle@xeno test]$ cat *.dbf > /dev/null [oracle@xeno test]$ fincore -justsummarize *.dbf page size: 4096 bytes 154788 pages, 604.6 Mbytes in core for 10 files; 15478.80 pages, 60.5 Mbytes per file. [oracle@xeno test]$
But not all is cached:
[oracle@xeno test]$ du -sh *.dbf 5.1M ble.dbf 431M sysaux01.dbf 551M system01.dbf 131M temp01.dbf 3.2M temp02.dbf 226M undotbs01.dbf 33M undotbs2.dbf 33M undotbs3.dbf 21M uniform2_01.dbf 348M users01.dbf [oracle@xeno test]$ [oracle@xeno test]$ fincore -justsummarize undotbs3.dbf page size: 4096 bytes 3029 pages, 11.8 Mbytes in core for 1 file; 3029.00 pages, 11.8 Mbytes per file. [oracle@xeno test]$ ls -alh undotbs3.dbf -rw-r----- 1 oracle oinstall 33M Feb 27 14:34 undotbs3.dbf [oracle@xeno test]$
And we have total ~917 MB cached in VM:
[oracle@xeno test]$ grep ^Cached /proc/meminfo Cached: 939208 kB [oracle@xeno test]$
The fincore uses mincore(2) syscall, and it appeared in the old days of 2.3.99pre1, so it should work on most of your old boxes, provided that somebody would get rid of that python dependency 