Hi all,
I have the following scenario:
- For a standalone snmp MASTER agent (Note: in order to troubleshoot the
problem explained below, I'm NOT using snmpd at all - no agentX neither
proxy) written in with net-snmp (ver 5.7 cross-compiled for PPC
processor) I have some snmp tables containing several lines (dynamic
sized: using rowStatus). The data to fill these tables is acquired
through IPC (for example: UDP socket msg sent from SNMP agent to an
server app that returns back data to agent). In other words: when the
agent receive a snmp get request, the request is forwarded to the server
app that returns back the data that is line based to the agent).
- MIB code was implemented upon
mib2c.iterate_access.conf/mib2c.access_functions.conf mib2c methodology
(exceptionally mib2c used to compile MIBs was from net-snmp 5.4.2.1, but
I don't think that it makes any significant difference).
Right now I realized that I have a very hard performance
problem:
- For example when one of the tables contains 130 lines for example, it
takes a very long time to collect data. This is caused due to the fact
that for every get-next, the whole table is collected from server app
(so to collect 130 lines, I'm having 130*130 IPC calls). If I'll have
1000 lines it will be almost impossible to collect data for this table!!
I tried to find a solution for this problem within net-snmp framework
itself without a whole code refactoring nor re-compiling the MIBs using
another methodology (for example MFD).
If I understood correctly the net-snmp docs I think that
caching/stash_cache could be a good solution in order to alleviate these
performance problems (as stated in doc, stashed cache may be used with
table iterators). However when trying to applying it: OR I did not
understood how to implement/apply this solution NEITHER it didn't work.
I'll explain what I tried to do:
(First of all: I understood that stash cache may cache OID results (for
a limited period of time, like 30 secs) in such a way that table
collection is made only once (for 130 lines: it will cache data results,
decreasing from 130 * 130 IPC calls to only 130) .
This cache is automatically built from data collected by net-snmp stash
cache engine with no needs to add anything to the code like
*_load.../*_free... functions used in other methods like the one in
netsnmp_get_cache_handler. stash cache is good only for 30 secs. Please
correct me if I misunderstand it.)
1) I found in documentation that stash cache may be added in
configuration file, so I've added the following line to .conf file:
injectHandler stash_cache onuCfgTable table_iterator
(where onuCfgTable is the name I gave in
netsnmp_create_handler_registration("onuCfgTable", ...) )
The table collection still work but no performance increase noted ( I
added printing withing onuCfgTable_get_first_data_point/
onuCfgTable_get_next_data_point, and I saw that still access was 130 *
130 times and even when trying to get the table again these functions
still were called 130 * 130 times).
2) I found another way to make the same thing, but in code:
netsnmp_inject_handler( my_handler, netsnmp_get_stash_cache_handler());
This method also not only did not worked, but it was worse: now no lines
were returned at all to MIB browser (it returned empty table for first
time or it returned snmp generic error for second try).
(I'm attaching a code snippet in order to clarify)
////////////////////////////////////////////////////////////////////////
/////////////////////////////////////
netsnmp_table_registration_info *table_info;
netsnmp_handler_registration *my_handler;
netsnmp_iterator_info *iinfo;
/** create the table registration information structures */
table_info = SNMP_MALLOC_TYPEDEF(netsnmp_table_registration_info);
iinfo = SNMP_MALLOC_TYPEDEF(netsnmp_iterator_info);
my_handler = netsnmp_create_handler_registration("onuCfgTable",
onuCfgTable_handler,
onuCfgTable_oid,
OID_LENGTH
(onuCfgTable_oid),
HANDLER_CAN_RWRITE);
if (!my_handler || !table_info || !iinfo) {
snmp_log(LOG_ERR, "malloc failed in
initialize_table_onuCfgTable");
return; /** Serious error. */
}
/***************************************************
* Setting up the table's definition
*/
netsnmp_table_helper_add_indexes(table_info, ASN_UNSIGNED,
/** index: XXXX */
ASN_UNSIGNED,
/** index: XXXX */
ASN_UNSIGNED,
/** index: XXXX */
0);
/** Define the minimum and maximum accessible columns. This
optimizes retrival. */
table_info->min_column = 4;
table_info->max_column = 61;
/** iterator access routines */
iinfo->get_first_data_point = onuCfgTable_get_first_data_point;
iinfo->get_next_data_point = onuCfgTable_get_next_data_point;
/** tie the two structures together */
iinfo->table_reginfo = table_info;
//iinfo->flags = NETSNMP_ITERATOR_FLAG_SORTED;
/***************************************************
* registering the table with the master agent
*/
DEBUGMSGTL(("initialize_table_onuCfgTable",
"Registering table onuCfgTable as a table iterator\n"));
netsnmp_register_table_iterator(my_handler, iinfo);
netsnmp_inject_handler( my_handler,
netsnmp_get_stash_cache_handler());
////////////////////////////////////////////////////////////////////////
/////////////////////////////////////
3) I found also that replacing netsnmp_inject_handler(
my_handler, netsnmp_get_stash_cache_handler()); with the following code
should also work:
netsnmp_inject_handler( my_handler,
netsnmp_get_timed_stash_cache_handler(30, onuCfgTable_oid,
OID_LENGTH(onuCfgTable_oid)));
But it still behaved exactly as the previous solution (empty
table + error).
I would be glad if someone could help me with an advice what
on some kind of solution that may be applied in this case in order to
increase performance without a big effort nor massive code re-writing).
Ivo
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