snmp_index(3erl)					     Erlang Module Definition						  snmp_index(3erl)

NAME

       snmp_index - Abstract Data Type for SNMP Indexing

DESCRIPTION

       The module snmp_index implements an Abstract Data Type (ADT) for an SNMP index structure for SNMP tables. It is implemented as an ets table
       of the ordered_set data-type, which means that all operations are O(log n). In the table, the key is an ASN.1 OBJECT IDENTIFIER.

       This index is used to separate the implementation of the SNMP ordering from the actual implementation of the table. The SNMP ordering, that
       is implementation of GET NEXT, is implemented in this module.

       For  example,  suppose  there is an SNMP table, which is best implemented in Erlang as one process per SNMP table row. Suppose further that
       the INDEX in the SNMP table is an OCTET STRING. The index structure would be created as follows:

       snmp_index:new(string)

       For each new process we create, we insert an item in an snmp_index structure:

       new_process(Name, SnmpIndex) ->
	 Pid = start_process(),
	 NewSnmpIndex =
	   snmp_index:insert(SnmpIndex, Name, Pid),
	 <...>

       With this structure, we can now map an OBJECT IDENTIFIER in e.g. a GET NEXT request, to the correct process:

       get_next_pid(Oid, SnmpIndex) ->
	 {ok, {_, Pid}} = snmp_index:get_next(SnmpIndex, Oid),
	 Pid.

COMMON DATA TYPES

       The following data types are used in the functions below:

	 * index()

	 * oid() = [byte()]

	 * key_types = type_spec() | {type_spec(), type_spec(), ...}

	 * type_spec() = fix_string | string | integer

	 * key() = key_spec() | {key_spec(), key_spec(), ...}

	 * key_spec() = string() | integer()

       The index() type denotes an snmp index structure.

       The oid() type is used to represent an ASN.1 OBJECT IDENTIFIER.

       The key_types() type is used when creating the index structure, and the key() type is used when	inserting  and	deleting  items  from  the
       structure.

       The  key_types() type defines the types of the SNMP INDEX columns for the table. If the table has one single INDEX column, this type should
       be a single atom, but if the table has multiple INDEX columns, it should be a tuple with atoms.

       If the INDEX column is of type INTEGER, or derived from INTEGER, the corresponding type should be integer . If it is a variable length type
       (e.g.  OBJECT  IDENTIFIER,  OCTET STRING), the corresponding type should be string . Finally, if the type is of variable length, but with a
       fixed size restriction (e.g. IpAddress), the corresponding type should be fix_string .

       For example, if the SNMP table has two INDEX columns, the first one an OCTET STRING with size 2, and the second one  an	OBJECT	IDENTIFER,
       the corresponding key_types parameter would be {fix_string, string} .

       The  key()  type correlates to the key_types() type. If the key_types() is a single atom, the corresponding key() is a single type as well,
       but if the key_types() is a tuple, key must be a tuple of the same size.

       In the example above, valid keys could be {"hi", "mom"} and {"no", "thanks"} , whereas "hi" , {"hi", 42} and {"hello",  "there"}  would	be
       invalid.

   Warning:
       All API functions that update the index return a NewIndex term. This is for backward compatibility with a previous implementation that used
       a B+ tree written purely in Erlang for the index. The NewIndex return value can now be ignored. The return value is now the unchanged table
       identifier for the ets table.

       The implementation using ets tables introduces a semantic incompatibility with older implementations. In those older implementations, using
       pure Erlang terms, the index was garbage collected like any other Erlang term and did not have to be deleted when discarded. An	ets  table
       is deleted only when the process creating it explicitly deletes it or when the creating process terminates.

       A  new  interface delete/1 is now added to handle the case when a process wants to discard an index table (i.e. to build a completely new).
       Any application using transient snmp indexes has to be modified to handle this.

       As an snmp adaption usually keeps the index for the whole of the systems lifetime, this is rarely a problem.

EXPORTS

       delete(Index) -> true

	      Types  Index = NewIndex = index()
		     Key = key()

	      Deletes a complete index structure (i.e. the ets table holding the index). The index can no longer be referenced	after  this  call.
	      See the warning note above.

       delete(Index, Key) -> NewIndex

	      Types  Index = NewIndex = index()
		     Key = key()

	      Deletes a key and its value from the index structure. Returns a new structure.

       get(Index, KeyOid) -> {ok, {KeyOid, Value}} | undefined

	      Types  Index = index()
		     KeyOid = oid()
		     Value = term()

	      Gets the item with key KeyOid . Could be used from within an SNMP instrumentation function.

       get_last(Index) -> {ok, {KeyOid, Value}} | undefined

	      Types  Index = index()
		     KeyOid = oid()
		     Value = term()

	      Gets the last item in the index structure.

       get_next(Index, KeyOid) -> {ok, {NextKeyOid, Value}} | undefined

	      Types  Index = index()
		     KeyOid = NextKeyOid = oid()
		     Value = term()

	      Gets  the  next  item  in  the SNMP lexicographic ordering, after KeyOid in the index structure. KeyOid does not have to refer to an
	      existing item in the index.

       insert(Index, Key, Value) -> NewIndex

	      Types  Index = NewIndex = index()
		     Key = key()
		     Value = term()

	      Inserts a new key value tuple into the index structure. If an item with the same key already exists, the new  Value  overwrites  the
	      old value.

       key_to_oid(Index, Key) -> KeyOid

	      Types  Index = index()
		     Key = key()
		     KeyOid = NextKeyOid = oid()

	      Converts Key to an OBJECT IDENTIFIER.

       new(KeyTypes) -> Index

	      Types  KeyTypes = key_types()
		     Index = index()

	      Creates a new snmp index structure. The key_types() type is described above.

Ericsson AB							     snmp 4.19							  snmp_index(3erl)