Logging Configuration

Michael A Leo (mal@adc.com) wrote:
: >
: >I'm in the process of setting-up a UNIX environment for a VMS based
: >Ingres database.  We'll be migrating the database to Sun machines in a
: >couple of months.  I'm interested in experiences, gotchas etc. from the
: >system administrators perspective.  I have an Ingres DBA and developers
: >to worry about the Ingres specific stuff, although I'll pass along any

	Stuff deleted.

: >info from the DBA perspective also:
: >2)  The default values for /etc/system that Ingres suggests, shared
: >memory etc.  Are these numbers
: >	OK, or has anyone found a better configuration?

	What isn't good in the Ingres default installation is the setup of the
	logging system.  One thing that can be a big performance bottleneck
	is the logging system - this can be checked with the logstat utility.

	This will show the total number of writes to the logging system
	and the number of these writes which had to wait for log buffers
	before being written to the log file and the number of writes that
	had to split log buffers to write.  I think the fields in logstat are
	"Log Waits" , "Log Free Waits" and "Log Split Waits".

	Increasing the number of log buffers from 4 to say 16, and the size
	of log buffers from 4k to 16k increases the amount of memory being 
	used to buffer writes to the log file from 16K total to 256K which
	can have a big impact on through-put of the I/O sub-system.

	On any Ingres installation doing even medium intensity I/O, you will
	get benefits from increasing the log buffers.  This is something that
	IMHO should be changed in the default setup.

	To change the log buffers, shut down ingres, then use csinstall to
	install the Ingres shared memory segments, then run

	rcpconfig -config  (from memory..)

	which will give the option to change the logging parameters.  If the
	log buffers are the only thing changed, the log file will _NOT_ be
	initialized so the job is quite quick.

: >3)  Raw disk - Apparently Ingres can only use a raw disk for logging,

	Yes, this will also improve performance.

Good Luck.

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|            Sean Riley - Australian in the USA.		  |
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