Stash cache - Revision history

Wes: /* Internal Details */

2011-07-15T22:41:47Z

‎Internal Details

Wes at 20:59, 15 July 2011

2011-07-15T20:59:23Z

Wes: Created page with "{{helper|Stash Cache|code=agent/helpers/stash_cache.c}} The '''stash_cache''' handler that can be injected either pragmatically or at run-time through the 'injectHandler' [[..."

2011-07-15T20:52:50Z

Created page with "{{helper|Stash Cache|code=agent/helpers/stash_cache.c}} The '''stash_cache''' handler that can be injected either pragmatically or at run-time through the 'injectHandler' [[..."

New page

{{helper|Stash Cache|code=agent/helpers/stash_cache.c}}

The '''stash_cache''' [[handler]] that can be injected either pragmatically or at run-time through the 'injectHandler' [[snmpd.conf]] configuration directive.

The purpose of the handler is to cache information from the lower sources, store it in an extremely fast searchable hash-tree, and return it to the agent any time new requests come in. The ''stash_cache'' handler needs to be injected above any table helper that takes care of normally returning data. Once the data is cached, it won't query the lower table handler again until the cache expires.

== Handler Types that Support The stash_cache ==

Right now the stash_cache is only usable with these handler types:

* [[table_iterator]]

== Usage ==

=== Programatically ===

In the modules code you can inject the handler as follows (usually after it's fully registered):

netsnmp_inject_handler_before(tptr->reginfo,
netsnmp_get_bare_stash_cache_handler(),
_clone_handler(handler),
"table_iterator");

You can also use the ''netsnmp_get_timed_bare_stash_cache_handler(...)'' function to create a handler with more specific timing parameters.

=== snmpd.conf ===

For tables that are implemented using a compliant handler, you can insert the stash cache at run-time using the following snmpd.conf syntax:

injectHandler stash_cache ''TABLE_NAME'' table_iterator

The ''table_iterator'' portion tells [[snmpd]] to inject the handler before the ''table_iterator'' part of the chain, which is required. Substitute a different handler type if the module is implemented using a different handler type.

== Internal Details ==

Internally, the stash cache intercepts GET and GETNEXT requests being sent down the handler chain. It will then:

* If the cache is present and recent, it will answer it and not call the lower handlers
* If the cache is out of date, it will create a new request with a special internal mode (''MODE_GET_STASH'')). The lower helper should extract the passed in [[oid_stash]] pointer and fill it with a complete copy of the table's data. IE, the lower handle doesn't just return a portion of the information, it needs to return '''everything'''!

← Older revision		Revision as of 22:41, 15 July 2011
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	* If the cache is present and recent, it will answer it and not call the lower handlers		* If the cache is present and recent, it will answer it and not call the lower handlers
	* If the cache is out of date, it will create a new request with a special internal mode (''MODE_GET_STASH'')). The lower helper should extract the passed in [[oid_stash]] pointer and fill it with a complete copy of the table's data. IE, the lower handle doesn't just return a portion of the information, it needs to return '''everything'''!		* If the cache is out of date, it will create a new request with a special internal mode (''MODE_GET_STASH'')). The lower helper should extract the passed in [[oid_stash]] pointer and fill it with a complete copy of the table's data. IE, the lower handle doesn't just return a portion of the information, it needs to return '''everything'''!
		+
		+	== Graphical Handler Chain ==
		+
		+	Graphically, before the stash_cache gets inserted the chain likely looks like this:
		+
		+	[[Image:before-stash-cache.png]]
		+
		+	And afterward:
		+
		+	[[Image:after-stash-cache.png]]

← Older revision		Revision as of 20:59, 15 July 2011
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−	{{helper\|Stash Cache\|code=agent/helpers/stash_cache.c}}	+	{{helper\|Stash Cache\|code=agent/helpers/stash_cache.c\|documentation=stash__cache}}

	The '''stash_cache''' [[handler]] that can be injected either pragmatically or at run-time through the 'injectHandler' [[snmpd.conf]] configuration directive.		The '''stash_cache''' [[handler]] that can be injected either pragmatically or at run-time through the 'injectHandler' [[snmpd.conf]] configuration directive.