Doc:latest/evalguide/csa103

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csa103 Checkpointing

Checkpointing refers to the practice of saving crucial program state in the cluster's "cloud" so that a standby process can resume operation without loss of state upon failure of the active process. This data is saved via the SAFplus Checkpointing APIs into what appears to be a simple key/value in-RAM database (like a hash table). But this "database" is actually replicated by our checkpointing servers and can be shared between multiple components.

Adding checkpointing to your application is simple. You first identify crucial program state and then you have the "active" process write it to a special key/value-database-like subsystem via the Checkpointing APIs. When the "standby" process becomes active, you read the checkpoint and update the program state before resuming service.

Objective

csa103 demonstrates the use of the SAFplus Checkpoint service to provide basic failure recovery. csa103 builds on csa102. The SAFplus Checkpoint service is SA-Forum compliant and this tutorial expects that you will refer to the SA-Forum document for an in-depth description of the checkpointing APIs used.

What Will You Learn

  • how to initialize the checkpoint client library,
  • how to create and open a checkpoint,
  • how to create a section in the checkpoint
  • how to write data to the checkpoint section
  • and read data from the checkpoint section.
  • how to extend the SAF dispatch loop to handle multiple libraries

The Code

The code can be found within the following directory 

<project-area_dir>/eval/src/app/csa103Comp

To increase readability, all checkpointing code has been isolated into a single module that consists of 2 files: checkpointFns.c and checkpointFns.h. These files provide the following APIs.

checkpointFns.h 
extern SaAisErrorT checkpoint_initialize(void);
extern void        checkpoint_finalize(void);
extern ClRcT       checkpoint_write_seq(ClUint32T);
extern ClRcT       checkpoint_read_seq(ClUint32T*);

These APIs constitute the basic operations of any messaging library; initialize, open, send and receive.

This file also declares some checkpoint handles as global variables and defines a "well-known" name for our checkpoint table. This simple example will only have a single row/key in the table (called a "section" in SA-Forum terminology), so we also define a well-known name for the row.

checkpointFns.h 
#define CKPT_NAME     "csa103Ckpt"    /* Checkpoint table name for this application  */
SaCkptHandleT  ckptLibraryHandle;     /* library hangle                              */
SaCkptCheckpointHandleT ckpt_handle;  /* Checkpoint table handle                     */
#define CKPT_SID_NAME "1"             /* Checkpoint section id                       */
extern SaCkptSectionIdT ckpt_sid;


Initialization

Initialization follows the standard SA-Forum library lifecycle pattern where before use an initialize call must occur that returns a handle that is used in subsequent library accesses.

In this example, we will both initialize the library and open the checkpoint table in the same function.

The following code excerpts handle the library initialization:

checkpointFns.c 
SaAisErrorT checkpoint_initialize(void)
{
    SaAisErrorT      rc = SA_AIS_OK;
    SaVersionT ckpt_version = {'B', 1, 1};
    SaCkptCallbacksT callbacks;

 ...

    /* These callbacks are only called when an Async style function call completes */
    callbacks.saCkptCheckpointOpenCallback        = checkpointOpenCompleted;
    callbacks.saCkptCheckpointSynchronizeCallback = checkpointSynchronizeCompleted;
        
    clprintf(CL_LOG_SEV_INFO,"Checkpoint Initialize");

        
    /* Initialize checkpointing library */
    rc = saCkptInitialize(&ckptLibraryHandle,	/* Checkpoint service handle */
                          &callbacks,			    /* Optional callbacks table */
                          &ckpt_version);   /* Required verison number */
    if (rc != SA_AIS_OK)
    {
        clprintf(CL_LOG_SEV_ERROR,"Failed to initialize checkpoint service with rc [%#x]", rc);
        return rc;
    }
    clprintf(CL_LOG_SEV_INFO,"Checkpoint service initialized (handle=0x%llx)", ckptLibraryHandle);
...
}

In this example, we register callbacks that are called when the asynchronous versions of the open and synchronize APIs are called. For threaded applications, it is simpler to use the default, synchronous APIs. The asynchronous versions are used in this example solely for expositional purposes.

Now let's focus on the portions that open the checkpoint table:

checkpointFns.c 
SaAisErrorT checkpoint_initialize(void)
{
    SaAisErrorT      rc = SA_AIS_OK;
    SaNameT    ckpt_name = { strlen(CKPT_NAME), CKPT_NAME };
    SaCkptCheckpointCreationAttributesT attrs;

    ...

    /* Set up the checkpoint configuration */
    attrs.creationFlags     = SA_CKPT_WR_ACTIVE_REPLICA_WEAK | SA_CKPT_CHECKPOINT_COLLOCATED;        
    attrs.checkpointSize    = sizeof(ClUint32T);
    attrs.retentionDuration = (ClTimeT) 10;        /* How long to keep the checkpoint around even if no one has it open */
    attrs.maxSections       = 2;                   /* Max number of 'rows' in the table */
    attrs.maxSectionSize    = sizeof(ClUint32T);   /* Max 'row' size */
    attrs.maxSectionIdSize  = (ClSizeT)64;         /* Max 'row' identifier size */

    ...    

    /* Create the checkpoint table for read and write. */
    rc = saCkptCheckpointOpen(ckptLibraryHandle,      // Service handle
                              &ckpt_name,         // Checkpoint name
                              &attrs,       // Optional creation attr.
                              (SA_CKPT_CHECKPOINT_READ |
                               SA_CKPT_CHECKPOINT_WRITE |
                               SA_CKPT_CHECKPOINT_CREATE),
                              (SaTimeT)SA_TIME_MAX,        // No timeout
                              &ckpt_handle);      // Checkpoint handle

    if (rc != SA_AIS_OK)
    {
        clprintf(CL_LOG_SEV_ERROR,"Failed [0x%x] to open checkpoint",rc);
        return rc;
    }
    clprintf(CL_LOG_SEV_INFO,"Checkpoint opened (handle=0x%llx)", ckpt_handle);
    return rc;
}

A checkpoint creation attributes structure is first defined and then its fields are set to define the behavior of the checkpoint. The definitions of these fields is beyond the scope of this guide, but are available in the SA-Forum checkpointing documentation.

Next, the saCkptCheckpointOpen function is called to open or create the checkpoint table. As the processes that constitute a redundant application start, their initialization routines are racing each other to create/open the table first. Therefore it is necessary to specify the SA_CKPT_CHECKPOINT_CREATE (in all processes) to ensure that whichever process wins will create the checkpoint.

Writing

Writing to a checkpoint section can fail if the section does not exist or if the process is not the checkpoint's "active replica". The active replica is essentially the checkpoint table's "master" copy and is only needed for checkpoints that are configured to allow only one writer. The active replica is assigned via a simple API call that is wrapped here:

checkpointFns.c 
ClRcT checkpoint_replica_activate(void)
{
    SaAisErrorT rc = SA_AIS_OK;

    if ((rc = saCkptActiveReplicaSet(ckpt_handle)) != SA_AIS_OK)
    {
        clprintf(CL_LOG_SEV_ERROR, "checkpoint_replica_activate failed [0x%x] in ActiveReplicaSet", rc);
    }
    else rc = SA_AIS_OK;

    return rc;
}

The application will call this API when the AMF tells it to become "active" for the CSI (work assignment), as shown in the "Putting it all Together" section.

The following code wraps the section write API. It first attempts to write the section and if that fails, the code creates the section.

checkpointFns.c 
SaAisErrorT checkpoint_write_seq(ClUint32T seq)
{
    SaAisErrorT rc = SA_AIS_OK;
    ClUint32T seq_no;
    
    /* Putting data in network byte order */
    seq_no = htonl(seq);
    
    /* Write checkpoint */
    rc = saCkptSectionOverwrite(ckpt_handle, &ckpt_sid, &seq_no, sizeof(ClUint32T));
    if (rc != SA_AIS_OK)
    {
        /* The error SA_AIS_ERROR_NOT_EXIST can occur either because we are not the active replica OR
           if the overwrite failed because the section did not exist then try to create the section.

           But in this case we know our application will not attempt to write unless it has set itself as
           the active replica so the problem MUST be a missing section.
        */
        if ((rc == 0x1000a) || (rc == SA_AIS_ERR_NOT_EXIST))
        {
            SaCkptSectionCreationAttributesT    section_cr_attr;
            
            /* Expiration time for section can also be varied
             * once parameters are read from a configuration file
             */
            section_cr_attr.expirationTime = SA_TIME_END;
            section_cr_attr.sectionId = &ckpt_sid;
            rc = saCkptSectionCreate(ckpt_handle,&section_cr_attr,(SaUint8T*) &seq_no, sizeof(ClUint32T));            
        }
        if (rc != SA_AIS_OK)
        {
            clprintf(CL_LOG_SEV_ERROR,"Failed [0x%x] to write to section", rc);
        }
    }

    if (rc == SA_AIS_OK)
    {
        /*
         * Synchronize the checkpoint to all the replicas.
         */
#if 0          /* Synchronous synchronize example */
        rc = saCkptCheckpointSynchronize(ckpt_handle, SA_TIME_END );
        if (rc != SA_AIS_OK)
        {
            clprintf(CL_LOG_SEV_ERROR,"Failed [0x%x] to synchronize the checkpoint", rc);
        }
#else
        rc = saCkptCheckpointSynchronizeAsync(ckpt_handle,syncCount);
        syncCount++;
        
#endif        
    }

    return rc;
}

The code also synchronizes the checkpoint. This synchronize operation ensures that all replicas have up-to-date data, and is only necessary for certain checkpoint configurations. In this case, the code demonstrates both the synchronous and asynchronous APIs. The async API is currently enabled simply do demonstrate the proper function of the combined AMF and checkpoint event dispatch loop (see the "Putting it all Together" section).

Reading

Reading the checkpoint is quite simple. The API allows for reads of multiple sections and allows subsets of the section's data to be read so an "IO-vector" style data structure is first initialized. To do multiple-section reads, this data structure should be an array of SaCkptIOVectorElementT. But in this example we only read a single section so an array is not needed.


checkpointFns.c 
ClRcT checkpoint_read_seq(ClUint32T *seq)
{
    SaAisErrorT rc = SA_AIS_OK;
    ClUint32T err_idx; /* Error index in ioVector */
    ClUint32T seq_no = 0xffffffff;
    SaCkptIOVectorElementT iov = {
        .sectionId  = ckpt_sid,
        .dataBuffer = (ClPtrT)&seq_no,
        .dataSize   = sizeof(ClUint32T),
        .dataOffset = (ClOffsetT)0,
        .readSize   = sizeof(ClUint32T)
    };
        
    rc = saCkptCheckpointRead(ckpt_handle, &iov, 1, &err_idx);
    if (rc != SA_AIS_OK)
    {
        if (rc != SA_AIS_ERR_NOT_EXIST)  /* NOT_EXIST is ok, just means no active has written */
            return SA_AIS_OK;
        
        clprintf(CL_LOG_SEV_ERROR,"Error: [0x%x] from checkpoint read, err_idx = %u", rc, err_idx);
    }

    *seq = ntohl(seq_no);
    
    return SA_AIS_OK;
}

It is important to handle the case of a missing section properly. Whether your application sees this error depends on the design of the application, but is a common design to see missing sections on application start because no prior "active" existed to fill the checkpoint. In this design, it is only on failover that the sections will have been written.

Putting it all Together

These functions are called from the application's clCompAppMain.c file to implement an application that simply prints a sequence count. But this count is checkpointed so it is not affected by process failure!

First, let's define what the program will do when it becomes active. The first step is to take over the "active replica" of the checkpoint so that the process can write the checkpoint. Next, it attempts to read the checkpoint to recover the last sequence number checkpointed by any prior "active" process. Finally, it enters the "active" loop and repeatedly increments the sequence number and writes the checkpoint.

clCompAppMain.c 
void* csa103CkptActive(ClPtrT unused)
{
    ClRcT rc = SA_AIS_OK;

    /* This thread will only be started when the application becomes active */
    assert(ha_state == SA_AMF_HA_ACTIVE);    

    clprintf(CL_LOG_SEV_INFO,"Active thread has started");
    /* Set this replica "active" so I can write to the checkpoint */
    if ((rc = saCkptActiveReplicaSet(ckpt_handle)) != SA_AIS_OK)
    {
        clprintf(CL_LOG_SEV_ERROR, "checkpoint_replica_activate failed [0x%x] in ActiveReplicaSet", rc);
    }

    /* Attempt to recover the state of the prior active */
    checkpoint_read_seq(&seq);
    
    while (!unblockNow)
    {
        clprintf(CL_LOG_SEV_INFO,"Hello World! (seq=%d)", seq++);            
        /* Checkpoint new sequence number */
        checkpoint_write_seq(seq);
        sleep(1);
    }
    return CL_OK;
}

Next, we move to the "main" function. In the initialization portion we will also initialize the checkpoint:


clCompAppMain.c 
...
   /*
     * Print out standard information for this component.
     */

    clEoMyEoIocPortGet(&iocPort);
    
    clprintf (CL_LOG_SEV_INFO, "Component [%.*s] : PID [%d]. Initializing\n", appName.length, appName.value, mypid);
    clprintf (CL_LOG_SEV_INFO, "   IOC Address             : 0x%x\n", clIocLocalAddressGet());
    clprintf (CL_LOG_SEV_INFO, "   IOC Port                : 0x%x\n", iocPort);

    checkpoint_initialize();
...

Next, we enter the dispatch loop. The auto-generated code creates a loop that handles the AMF processing. This generated loop has been extended to also handle checkpoint processing. Note that it is also perfectly acceptable (even easier) to spawn 2 threads and have one handle the AMF dispatches and the other checkpoint dispatches. This code has been implemented in this manner to show how it can all be done in a single thread.

clCompAppMain.c 
    /*
     * Block on AMF dispatch file descriptor for callbacks
     */
    if (1)
    {
        
        SaSelectionObjectT amf_dispatch_fd;
        SaSelectionObjectT ckpt_dispatch_fd;
        int maxFd;
        fd_set read_fds;

        /*
         * Get the AMF dispatch FD for the callbacks
         */
        if ( (rc = saAmfSelectionObjectGet(amfHandle, &amf_dispatch_fd)) != SA_AIS_OK)
            goto errorexit;
        if ( (rc = saCkptSelectionObjectGet(ckptLibraryHandle, &ckpt_dispatch_fd)) != SA_AIS_OK)
            goto errorexit;
    
        maxFd = max(amf_dispatch_fd,ckpt_dispatch_fd);
        do
        {
            FD_ZERO(&read_fds);
            FD_SET(amf_dispatch_fd, &read_fds);
            FD_SET(ckpt_dispatch_fd, &read_fds);
        
            if( select(maxFd + 1, &read_fds, NULL, NULL, NULL) < 0)
            {
                char errorStr[80];
                int err = errno;
                if (EINTR == err)
                {
                    continue;
                }
                errorStr[0] = 0; /* just in case strerror does not fill it in */
                strerror_r(err, errorStr, 80);
                clprintf (CL_LOG_SEV_ERROR, "Error [%d] during dispatch loop select() call: [%s]",err,errorStr);
                break;
            }
            if (FD_ISSET(amf_dispatch_fd,&read_fds)) saAmfDispatch(amfHandle, SA_DISPATCH_ALL);
            if (FD_ISSET(ckpt_dispatch_fd,&read_fds)) saCkptDispatch(ckptLibraryHandle, SA_DISPATCH_ALL);
        }while(!unblockNow);      
    }

Finally, when this application becomes active, we need to kick off the csa103CkptActive function in a new thread:


clCompAppMain.c 
        case SA_AMF_HA_ACTIVE:
        {
            /*
             * AMF has requested application to take the active HA state 
             * for the CSI.
             */
            clprintf(CL_LOG_SEV_INFO,"Active state requested from state %d", ha_state);
            
            ha_state = SA_AMF_HA_ACTIVE;

            pthread_t thr;
            pthread_create(&thr,NULL,csa103CkptActive,NULL);
            
            saAmfResponse(amfHandle, invocation, SA_AIS_OK);
            break;
        }


In this example, there is nothing to do while the process is assigned standby. This actually can be a problem; if the checkpoint is large it may take quite some time for the newly-assigned active process to completely read and process the checkpoint. The standby can read the checkpoint but how can it determine what it needs to read; what sections the active has changed?

Thus the SA-Forum checkpoint definition is not a "cold standby" because the process is running, but it is also not quite "hot"; we call it a "warm-standby".

But the OpenClovis SAFplus Platform provides an extension to the SA-Forum checkpoint definition that realizes true hot standby behavior. This extension will call an application registered call-back function whenever the active writes the checkpoint with all the write information. This allows the standby to remain in sync with the active so the checkpoint does not need to be read upon failover.

How to Run csa103 and What to Observe

This sample application can run on all Runtime Hardware Setups. The following, lists which node csa103compI* runs on.

  • Runtime Hardware Setup 1.1 and 2.1
    csa103compI0 and csa103compI1 will run upon the single node.
  • Runtime Hardware Setup 1.2 and 2.2
    csa103compI0 runs on PayloadNodeI0 and csa103compI1 runs on PayloadNodeI1
  • Runtime Hardware Setup 1.3 and 2.3
    csa103compI2 and csa103compI3 run on SCNodeI0 and SCNodeI1 respectively. csa103compI0 and csa103compI1 run on PayloadNodeI0 and PayloadNodeI1 respectively.

    In the four node set up SCNodeI0 and SCNodeI1 output data via /root/asp/var/log/csa103CompI2 and /root/asp/var/log/csa103CompI3 respectively. Therefore in this case follow the below instructions replacing csa103CompI0 and csa103compI1 with csa103compI2 and csa103compI3 respectively.

Just like all the "eval" programs, you need to compile, make images, deploy and then start the SAFplus platform on your target machines. This tutorial will specifically use the single node configuration since that is the simplest for evaluation purposes.

CSA103 is "unlocked" (running with work assigned) by default but (in review) this is what you can do to start/stop the application with the SAFplus Platform Console:

  1. First, on the active System Controller move it to state LockAssignment with (Unlock csa203SGI0 instead of csa103SGI0 to run csa203) 
    cli[Test]-> setc 1
cli[Test:SCNodeI0]-> setc cpm
cli[Test:SCNodeI0:CPM]-> amsLockAssignment sg csa103SGI0

    The following output is given when you run tail -f on both of the csa103 log files simultaneously: 

    # tail -f var/log/csa103CompI?Log.latest
    /root/asp/var/log/csa103CompI0Log.latest 
    root@gh-lubuntu1204:~/eval# tail -f var/log/csa103CompI?Log.latest
==> var/log/csa103CompI0Log.latest <==
Tue Jan 15 15:47:23.778 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00051 :   INFO) Hello World! (seq=29)
Tue Jan 15 15:47:23.779 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00052 :   INFO) Checkpoint synchronize [30] completed 
Tue Jan 15 15:47:24.778 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00053 :   INFO) Hello World! (seq=30)
Tue Jan 15 15:47:25.779 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00054 :   INFO) Hello World! (seq=31)
Tue Jan 15 15:47:26.780 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00055 :   INFO) Hello World! (seq=32)
Tue Jan 15 15:47:27.781 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00056 :   INFO) Hello World! (seq=33)
Tue Jan 15 15:47:28.783 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00057 :   INFO) Hello World! (seq=34)
Tue Jan 15 15:47:29.784 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00058 :   INFO) Hello World! (seq=35)
Tue Jan 15 15:47:30.785 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00059 :   INFO) Hello World! (seq=36)
Tue Jan 15 15:47:31.785 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00060 :   INFO) Hello World! (seq=37)

==> var/log/csa103CompI1Log.latest <==
OpenClovis_Logfile

==> var/log/csa103CompI0Log.latest <==
Tue Jan 15 15:47:32.786 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00061 :   INFO) Hello World! (seq=38)
Tue Jan 15 15:47:33.787 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00062 :   INFO) Hello World! (seq=39)
Tue Jan 15 15:47:33.788 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00063 :   INFO) Checkpoint synchronize [40] completed 
Tue Jan 15 15:47:34.788 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00064 :   INFO) Hello World! (seq=40)
Tue Jan 15 15:47:35.788 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00065 :   INFO) Hello World! (seq=41)

    So here we see that csa103CompI0 is the master and is currently counting upwards. Next, let us kill this process (the process ID is in the logs, just after the node name -- in this case 4276) while simultaneously "tailing" the logs:


    /root/asp/var/log/csa103CompI?Log.latest 
    Tue Jan 15 15:55:36.237 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00593 :   INFO) Hello World! (seq=521)
Tue Jan 15 15:55:37.237 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00594 :   INFO) Hello World! (seq=522)
Tue Jan 15 15:55:38.238 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00595 :   INFO) Hello World! (seq=523)
Tue Jan 15 15:55:39.239 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00596 :   INFO) Hello World! (seq=524)
Tue Jan 15 15:55:40.240 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00597 :   INFO) Hello World! (seq=525)
Tue Jan 15 15:55:41.241 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00598 :   INFO) Hello World! (seq=526)
Tue Jan 15 15:55:42.242 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00599 :   INFO) Hello World! (seq=527)

==> var/log/csa103CompI1Log.latest <==
OpenClovis_Logfile

==> var/log/csa103CompI0Log.latest <==
Tue Jan 15 15:55:43.243 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00600 :   INFO) Hello World! (seq=528)
Tue Jan 15 15:55:44.244 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00601 :   INFO) Hello World! (seq=529)
Tue Jan 15 15:55:44.245 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00602 :   INFO) Checkpoint synchronize [530] completed 
Tue Jan 15 15:55:45.244 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00603 :   INFO) Hello World! (seq=530)
Tue Jan 15 15:55:46.245 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00604 :   INFO) Hello World! (seq=531)
Tue Jan 15 15:55:47.246 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00605 :   INFO) Hello World! (seq=532)
Tue Jan 15 15:55:48.247 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00606 :   INFO) Hello World! (seq=533)
Tue Jan 15 15:55:49.248 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00607 :   INFO) Hello World! (seq=534)
Tue Jan 15 15:55:50.249 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00608 :   INFO) Hello World! (seq=535)
Tue Jan 15 15:55:51.250 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00609 :   INFO) Hello World! (seq=536)
Tue Jan 15 15:55:52.250 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00610 :   INFO) Hello World! (seq=537)
Tue Jan 15 15:55:53.251 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00611 :   INFO) Hello World! (seq=538)
Tue Jan 15 15:55:54.252 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00612 :   INFO) Hello World! (seq=539)
Tue Jan 15 15:55:54.253 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00613 :   INFO) Checkpoint synchronize [540] completed 
Tue Jan 15 15:55:55.253 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00614 :   INFO) Hello World! (seq=540)
Tue Jan 15 15:55:56.254 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00615 :   INFO) Hello World! (seq=541)
Tue Jan 15 15:55:57.254 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00616 :   INFO) Hello World! (seq=542)
Tue Jan 15 15:55:58.255 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00617 :   INFO) Hello World! (seq=543)
Tue Jan 15 15:55:59.257 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00618 :   INFO) Hello World! (seq=544)
Tue Jan 15 15:56:00.258 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00619 :   INFO) Hello World! (seq=545)
Tue Jan 15 15:56:01.259 2013 (SCNodeI0.4276 : csa103CompEO0.---.---.00620 :   INFO) Hello World! (seq=546)

==> var/log/csa103CompI1Log.latest <==
Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00016 :   INFO) Component [csa103CompI1] : PID [4275]. CSI Set Received

Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00017 :   INFO) CSI Flags : [Target All]
Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00018 :   INFO) HA state : [Active]
Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00019 :   INFO) Active Descriptor :
Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00020 :   INFO) Transition Descriptor : [3]
Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00021 :   INFO) Active Component : [csa103CompI0]
Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00022 :   INFO) Active state requested from state 2
Tue Jan 15 15:56:01.287 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00023 :   INFO) Active thread has started
Tue Jan 15 15:56:01.289 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00024 :   INFO) Hello World! (seq=547)
Tue Jan 15 15:56:01.290 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00025 :   INFO) Checkpoint synchronize [0] completed 

==> var/log/csa103CompI0Log.latest <==
Tue Jan 15 15:56:01.320 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00001 :   INFO) Component [csa103CompI0] : PID [5621]. Initializing

Tue Jan 15 15:56:01.320 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00002 :   INFO)    IOC Address             : 0x1

Tue Jan 15 15:56:01.320 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00003 :   INFO)    IOC Port                : 0x89

Tue Jan 15 15:56:01.320 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00004 :   INFO) Checkpoint Initialize
Tue Jan 15 15:56:01.323 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00005 :   INFO) Checkpoint service initialized (handle=0x1000900000001)
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00006 :   INFO) Checkpoint opened (handle=0x1000900000002)
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00007 :   INFO) Component [csa103CompI0] : PID [5621]. CSI Set Received

Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00008 :   INFO) CSI Flags : [Add One]
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00009 :   INFO) CSI Name : [csa103CSII0]
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00010 :   INFO) Name value pairs :
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00011 :   INFO) HA state : [Standby]
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00012 :   INFO) Standby Descriptor :
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00013 :   INFO) Standby Rank : [1]
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00014 :   INFO) Active Component : [csa103CompI1]
Tue Jan 15 15:56:01.324 2013 (SCNodeI0.5621 : csa103CompEO0.---.---.00015 :   INFO)  Standby state requested from state 0

==> var/log/csa103CompI1Log.latest <==
Tue Jan 15 15:56:02.290 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00026 :   INFO) Hello World! (seq=548)
Tue Jan 15 15:56:03.291 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00027 :   INFO) Hello World! (seq=549)
Tue Jan 15 15:56:04.292 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00028 :   INFO) Hello World! (seq=550)
Tue Jan 15 15:56:05.293 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00029 :   INFO) Hello World! (seq=551)
Tue Jan 15 15:56:06.294 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00030 :   INFO) Hello World! (seq=552)
Tue Jan 15 15:56:07.296 2013 (SCNodeI0.4275 : csa103CompEO0.---.---.00031 :   INFO) Hello World! (seq=553)
...

    What these logs show is process 4276 as active up to sequence number 546. Then I killed the process and so the AMF assigned process 4275 as active. This process read the checkpoint and continued with sequence number 547. Next, the AMF restarted the killed component as process 5621 and assigned it standby. Finally the system entered into a steady state with process 4275 as active and 5621 as standby.

    Next, you can try killing the active again, or the standby and examine the behavior of the system.


    To stop csa103 use the following SAFplus Platform Console command: 

    cli[Test:SCNodeI0:CPM]-> amsLockAssignment sg csa103SGI0

    Now change the state of csa103SGI0 to LockInstantiation and close the SAFplus Platform Console. 

    cli[Test:SCNodeI0:CPM]-> amsLockInstantiation sg csa103SGI0
cli[Test:SCNodeI0:CPM] -> end
cli[Test:SCNodeI0] -> end
cli[Test] -> bye

Additional Experiments

  • In the multi-node configuration, you can try a node failure instead of a process failure. To do this, either run "etc/init.d/safplus stop" or power the node off.
  • Have the active write to more than one checkpoint section.
  • Study and experiment with the other checkpoint modes -- collocated verses non-collocated and asynchronous verses synchronous.
  • Examine the SAFplus hot-checkpoint extension. Please contact us for a hot-checkpoint example application.

Summary and References

We've seen :

  • how to use the OpenClovis SAFplus checkpoint service to save some program state and recover that state from a separate process
  • how to initialize the client checkpoint library
  • how to integrate the checkpoint with the AMF active/standby work assignments so that the "active" process recovers prior checkpoint data and becomes the active replica.
  • how to create and open checkpoints
  • how to create and use sections in an opened checkpoint
  • how to use a single dispatch loop to handle dispatches for multiple libraries.

Further information can be found within the following: OpenClovis API Reference Guide.

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