[snmp] customisable oid_batch_size batch size

[yannmh]

Here is a 5.5.2 candidate

Context

For an unindentified reason (need more investigation ?), some OIDs do not return when pulled in a batch query. By default, the SNMP AgentCheck attemps to query up to 10 OID at the same time to speed up the crawling runtime.

Example

Running SNMP command nextCmd on OIDS ('1.3.6.1.4.1.39538.3.1.3.1.1.7', '1.3.6.1.4.1.39538.3.1.3.3.1.11') 
Returned vars: [[(ObjectName('1.3.6.1.4.1.39538.3.1.3.1.1.7.0'), Integer(7)), (ObjectName('1.3.6.1.6.3.1.1.6.1.0'), Integer(1694833796))]]

(Note the unrelated '1.3.6.1.6.3.1.1.6.1.0' returned 😮 )

versus

Running SNMP command nextCmd on (CommunityData(communityIndex='s1542604247011267360', communityName=<COMMUNITY>, mpModel=1, contextEngineId=None, contextName='', tag='', securityName='s1542604247011267360'), UdpTransportTarget(('127.0.0.1', 161), timeout=1, retries=5, tagList=''), '1.3.6.1.4.1.39538.3.1.3.3.1.11') | {'lookupValues': False, 'lookupNames': False}
Returned vars: (None, Integer('noError', NamedValues(('noError', 0), ('tooBig', 1), ('noSuchName', 2), ('badValue', 3), ('readOnly', 4), ('genErr', 5), ('noAccess', 6), ('wrongType', 7), ('wrongLength', 8), ('wrongEncoding', 9), ('wrongValue', 10), ('noCreation', 11), ('inconsistentValue', 12), ('resourceUnavailable', 13), ('commitFailed', 14), ('undoFailed', 15), ('authorizationError', 16), ('notWritable', 17), ('inconsistentName', 18))), Integer(0, subtypeSpec=ConstraintsIntersection(ConstraintsIntersection(), ValueRangeConstraint(0, Integer(2147483647)))), [[(ObjectName('1.3.6.1.4.1.39538.3.1.3.3.1.11.0'), Integer(3))]])

Changes

Make the OID batch size configurable. Create a 'hidden' oid_batch_size option in the init_config section of the check YAML configuration file (default to 10).
Helpful to troubleshoot and workaround batch query related cases.

[remh]

Shouldn't it be at the instance level instead ?

[yannmh]

Not sure what's better, I purposely made this parameter settable at the check level. I can move it to an instance level instead,