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version 1.1.2.1, 2011/01/16 21:11:30

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Using the CIM/XML Pull Operations

STATUS

<<< This section is being maintained during the review and checkin process

to keep track of problems, errors, notes, etc. Must be deleted before

checkin to head of tree. Please feel free to add notes, etc in this

section as you review/test.>>>>>>

16 Jan 2011

Issues - KS

1. have not installed the binary move in CIMResponseData. Please run

with OPP off.

2. Some problem in the processing so we are getting server crashes.

Right no I am guessing that this is in the binaryCodec and am going to

expand the test tools to allow testing through the localhost.

3. Still way to many TODO and KS comments and KS_TEMPS. Removing bit by bit.

4. Env variable connection for the config parameters not installed.

5. Issue with the threaded timer. For some reason during tests it

eventually calls the timer thread with trash for the parm (which is

pointer to the EnumerationTable object). Caught because we do a valid

test at beginning of the function.

===========================================

OVERVIEW:

The operation extensions for pull operations defined in the DMTF specification

DSP0200 V 1.4 were implemented in Pegasus effective Pegasus version 2.11

including Client and Server.

These operations extend the CIM/XML individual operations to operation

sequences where the server must maintain state between operations in a

sequence and the client must execute multiple operations to get the full

set of instances or instance paths.

The following new CIM/XML operations as defined in DSP0200 are included;

-OpenEnumerateInstances

-openEnumerateInstancePaths

-OpenReferenceInstances

-OpenReferenceInstancePaths

-OpenAssociatiorInstances

-OpenAssociatorInstancePaths

-PullInstancesWithPath

-PullInstancePaths

-CloseEnumeration

-EnumerationCount

The following operations have not been implemented in this version of Pegasus:

-OpenQueryInstances

The following limitations on the implementation exist;

1. The filterQueryLanguage and filterQuery parameters are processed by

the Pegasus client but the server returns error if there is any data in

either parameter. This is because the definition of query language has not

been clarified to date by the DMTF.

2. The input parameter continueOnError is processed correctly by the client

but the Pegasus server only provides for false since the server does not

include logic to continue processing responses after an error is

encountered.

This is consistent with the statement in the specification that use of

this functionality is optional and the fact that the DMTF agrees that all

of the issues of continuing after errors have not been clarified.

3. The operation enumerationCount is not processed by the server today since

a) really getting the count would be the same cost as the corresponding

enumeration, b) the server does not include a history or estimating

mechanism for this to date.

KS_TBD_ confirm this

Since the concept of sequences of operations linked together (open, pull, close)

is a major extension to the original CIM/XML operation concept of completely

independent operations several new pieces of functionality are implemented

to control interOperationTimeouts, counts of objects to be returned, etc.

TBD - Review this

CLIENT

The new operations follow the same pattern as the APIs for existing operations

in that:

1. All errors are handled as CIMException and Exception

2. The means of inputting parameters are the same except that there are

significantly more input parameters with the open operations and for the

first time operations return parameters as well as objects in the

response. Specifically the open and pull operations return values for

enumerationContext which is the identity for a pull sequence and

endOfSequence which is the marker the server sends in open and pull

responses when it has no more objects to send.

The significant differences include:

1. Processing of parameters on responses (i.e. the endOfSequence and

enumerationContext parameters are returned for open and pull operations).

2. Numeric arguments (Uint32 and Uint64 include the option of NULL in some

cases so they are packaged inside classes Uint32Arg and Uint64Arg in the

client api.

3. The association and reference operations ONLY process instances. They do

not include the capability to return classes like reference and associator

do and therefore return CIMInstance rather than CIMObject.

4. Paths are returned in all cases (i.e OpenEnumerateInstances and

PullInstancesWithPath where they were not with EnumeratInstances.

5. The client must maintain state between operations in a sequence (using

the enumerationContext parameter).

TBD- Are there more differences.

SERVER

The Pegasus server attempts to always deliver the requested number of objects

for any open or pull request (the specification allows for the server to

deliver less than the requested number of objects and specifically to return

zero objects on open). We felt that it was worth any extra cost in processing

to provide the client with exactly what it had requested.

continueOnError Parameter

The pegasus server always closes an enumeration sequence upon receipt of any

error from the providers, repository, etc. Therefore the server will reject

and request that has continueOnError = true;

PROVIDERS

This implementation requires NO changes to the existing providers. The

provider APIs operate just as they do with the original operations.

Because the server processing is different however, there may be some

behavior differences primarily because the client now controls the speed of

delivery of objects.

In previous versions of Pegasus, the server attempts to deliver objects as

rapidly as then can be put on the network. In the case of HTTP chunked requests

they are delivered in chunks of about 100 objects. The primary delay for the

providers was the processing of each segment through the server. The server

is blocked so that no other segment can proceed through the server until that

segment is processed and sent on the network.

In the case of non-chunkedresponses, they are completely gathered in the serve

and then delivered as one non-chunked response. There were no delays for the

providers, just lots of possible memory use in the server.

The responses from providers (delivered through the deliver(...) interface are

gathered into segments of about 100 objects and this group of objects is moved

through the server to be delivered to the client.

However with the inclusion of the pull operations, The segments of objects

from the providers are cached in the server response path until the

maxObjectCount for that request (open or pull) and that number returned in a

non-chunked response. Thus, if the client is slow to issue pull requests,

the providers might be delayed at some point to reduce memory usage in the

server (the delay appears as slow response tothe deliver operation).

In other words, the time to process large sets of responses from the provider

now depends on the speed of handling the client.

It is important to remember in developing providers that the Pegasus server

can most efficiently process responses if they are passed from the provider

to the server individually or in small arrays of objects rather than the

provider gathering very large arrays of objects and sending them to the

server.

CONFIGURATION PARAMETERS

The server includes several configuration parameters to set limits on the

processing of pull operations. All of these configuration parameters are

compile time parameters rather than runtime.

1. Maximum value of minimum interoperation time. This parameter defines the

maximum time allowed between the return of an open or pull response and

the receipt of the next pull or a close operation before the server may

close the enumeration. The specification allows the server to set a

maximum interoperation time and refuse open requests that with requested

operationTimeout greater than that time.

CIM_ERR_INVALID_OPERATION_TIMEOUT

This value is set with the Pegasus environment variable

PEGASUS_PULL....

2. Maximum objects returned in a single open or pull operation. The server

can set a maximum limit on the number of objects that can be returned in

a single open or pull oepration with the maxObjectCount parameter.

3. Whether the server allows 0 as an interoperation timeout value. The value

zero is s special value for the interoperationTimeout in that it tells the

server to not timeout any enumeration sequence.

With this value for interoperationTimeout, the only way to close an

enumeration sequence is to complete all of the pulls or issue the close.

If for some reason the sequence is not completed, that enumeration context

would remain open indefinitly. Since in Pegasus any open enumeration

context uses resources (the context object and any provider resposnes that

have not yet been issued in a response) it would appear that most

platforms would not want to allow the existence of enumeration contexts

that cannot be closed by the server.

4, maximum consecutive pull requests with 0 maxObjectCount. The use of the

pull operation with maxObjectCount set to zero could be used to keep an

enumeration context open indefinitly (this tells the server to restart the

interoperationTimeout but not send any objects in the response). Therefore the

specification allows for the server setting maximum limits on this behavior

and returning the error CIM_ERR_SERVER_LIMITS_EXCEEDED if this limit is

exceeded.

Note that this is maximum CONSECUTIVE pulls so that issuing a pull with

a non-zero count resets this counter.

KS-TBD - Is this really logical since we can still block by just issuing

lots of zero request and an occansional request for one object.

Pegaus sets the value of this limit to 1000 and allows the implementer to

modify it with the PEGASUS_MAXIMUM_ZERO_OBJECTCOUNT environment variable.

5. Default operationTimeout -

The default of this parameter is to refuse operat

In the current release of Pegasus these are all compile time parameters.

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