Ns2 project in sheffield

      Ns2 project in Sheffield this analysis thus estimates perturbation per notification generated, using subexpression selectivities, that is, given the subexpressions in the action predicate, the actual percentage of their evaluations resulting ns2 project in Sheffield in the value “true.” To summarize, we propose a four-step process to generate code from a view specification. First, all feasible view implementation plans are generated. This is ns2 project in Sheffield done either by simply enumerating all possible plans and then eliminating those that do not pass fairly simple correctness checks, orby applying the checks during the enumeration ns2 project in Sheffield to avoid enumerating entire groups of incorrect plans.

       The second step filters outthose plans that do not meet latency constraints. This step employs ns2 project in Sheffield an analytical model that estimates the per event record latency. Inaccuracies in the model may eliminate some plans that meet these constraints. On the other hand, all remaining plans ns2 project in Sheffield will be correct. The third step partitions the remaining plans into collections of plans ns2 project in Sheffield that generate approximately the same number of event records. The most efficient plan in each collection is selected, based on a per event record analytical model of the CPUoverhead.

      This model is quite accurate. In the fourth and final step, one plan ns2 project in Sheffield is selected from those that remain based on an informal analysis that ns2 project in Sheffield takes into account both the per event record perturbation and the number of event records generated. However, the inaccuracy will manifest itself in less efficient data collection, rather ns2 project in Sheffield than incorrect data collection. Also, at this point, only a few plans are being considered; the vast majority of initially generated plans having been eliminated by application of more accurate analyses.

Ns2 project in oxford

      Ns2 project in oxford applyingpereventrecordperturbationanalysis. After  have been performed, the remainingview implementation plans are correct, but they can differmarkedly in performance. In this step, the monitor applies ans2 project in oxford simple analytical model, similar to that for latency, to estimatethe perturbation each plan would impose on the executingapplication process.

     This model must be applied carefully,as ns2 project in oxford the absolute perturbation, expressed as the total CPU cost added to the execution time of the application process, depends on the total number of event records generated, ns2 project in oxford which of course is unknown a priori. The perturbation model is applied by partitioning all remainingplans into collections. Each plan in a collection will generate approximately the ns2 project in oxford same number of event records as other plans in that collection. Then, for each plan, the CPU overhead is estimated for the processor on which the application process is executing  overhead on processors dedicated to monitoring will not perturb the application.

     This estimate ns2 project in oxford is on a pereventrecordbasis, and is thus quite accurate. Those plans with an estimate higher than the minimum for the collection are eliminated, leaving one plan per collection. In our example, there would be collections, with these two plans in different ns2 project in oxford collections which would have an identicalcost per event record. Atthis point, plans differ in both their perturbation per event record andin the number of event records generated. To make a final choice, the monitor must estimate the relative number of ns2 project in oxfordevent records generated amongthe altemative plans.

Ns2 project in nottingham

     Ns2 project in Nottingham the notification latency is estimated at, significantly less than the requested. Similar analyses for this view implementation plan mapped to the Encore Multimax and to the GEM real-time operating ns2 project in Nottingham system executing on an Intel-based multiprocessor would showthat the specified latency constraints would be met ns2 project in Nottingham there as well. Now consider the second view implementation plan presented above, where the value in QueueManage is probed, when executed on the same local area network.

      When the value of queuesizein QueueManagerexceeds ns2project in Nottingham the sensor sends a message to the monitor, which takes approximately The monitor then probes the value of queuesizein QueueManager. If QueueManagerresides on a different ns2 project in Nottingham node, then probing takes approximately  messages,  intranode and  internode messages, or about. Since is less than the specified correctness value of, this plan also satisfies the latency constraint. Note, however, if the user had instead specified CORRECTTOWITHIN , the ns2 project in Nottingham first plan would havebeen acceptable, but the second one would not have been.

      The accuracy of the model is important only when the estimate is similar to the latency constraint specified by the user. In the example above, the model could have been off by ns2 project in Nottingham without changing the result of accepting both plans. Our general strategy has been to apply the model conservatively, recognizing that some plans ns2 project in Nottingham may nevertheless be prematurely rejected due to inaccuracies in the model, with another ns2 project in nottingham plan chosen that also meets the latency constraint yet perhaps exhibits greater perturbation.

Ns2 project in Australia

        Ns2 project in Australia applyinglatencyconstraints. Two latency constraints may be specified: CORRECT WITHIN and NOTIFY WITHIN. For each feasible view implementation plan produced by the first step, the monitor applies a simple analytic ns2 project in Australia model to estimate the delay between the occurrence of the event and either the evaluation of the action predicate  or the receipt of notification. The model ns2 project in Australia includesestimates of CPU time to process messages and perform analyses, as well as estimates of message transmission time. Details of the analytical model, as well as i ns2 project in Australia ts validation, are given elsewhere .

     Here we will apply the model to the two sample feasible view implementation plans discussed above. For the first one, the latency ns2 project in Australia involves the time to execute the sensor, the time to transmit the event record to the resident monitor and then to the central monitor, the processing involved in the resident and central monitors for this message transmission, and the ns2 project in Australia time to perform the analysis at the central monitor and to send a notification message.

      For the ns2 project in Australia distributed Unix implementation of the monitoring system, message transmission was measured as roughly  ms between processes on the same machine,  ms between processes on the same subnet, and 10 ms between processes across ns2 project in Australia multiple subnets under conditions of low Ethernet traffic. Each event record is first sent to the resident monitor on the same machine  and then to the central monitor . The ns2 project in Australia total processing cost, dominated by several context switches, is less than 2 ms, implying a total latency on the order of 15 ms, which is less than the specified.

Ns2 project in canada

     Ns2 project in Canada afundamental requirement of any generated view implementation plan, termed a feasible plan, is that it preserve the semantics of the target list and action predicate  While both of the plans outlined above are fine in this regard, the ns2 project in Canada following is not, assuming an environment consisting of workstations communicating via an Ethernet. Trace the value of the variables recording the queue ns2 project in Canada size in both QueueManager and Queuemanager, and evaluate the action predicate in the resident monitor. Since QueueManager and QueueManagermay be executing on ns2 project in Canada different workstations, event records from both may never be present within any ns2 project in Canada one resident monitor, preventing the evaluation of the action predicate.

        To ns2 projects in Canada generate all possible view implementation plans, the monitor’s compiler should incorporate all of the following choices in all possible combinations: sampling, ns2 project in canada tracing, or probing the value of each attribute mentioned in the view; performing each subexpression in the sensor, in the resident monitor, or in the central monitor; ns2 project in Canada having each sensor send records to the resident monitor or directly to the ns2 projects in Canada central monitor; and generating notifications only in the central monitor or also in the resident monitor.

      In the sample view, there are two attributes mentioned, and three ns2 project in Canada possible subexpressions, generating approximately view implementation plans. Clearly, the ns2 project in Canada space of all possible view implementation plans may be very large for complex views or architectures. Enumerating the feasible plans may be simplified by eliminating ns2 projects in Canada easily detected infeasible plans until the third step, and by ns2 project in Canada reorganizing the action predicate so that variables from the same entity occur together in the subexpressions.

Ns2 project in New York

         Ns2 project in New York however, such centralized analysis is again limited due to restrictions in the bandwidths of sensor to resident monitor to central monitor communications. A four step analysis, analogous to ns2 project in New York that used in query optimization in traditional database management systems,may be followed during the generation of collection and analysis code distributed across the application program ns2 project in New York and the monitoring syste Generate all possible viewimplementationplans that preserve the semantics of the target list and of the action predicate.

        Discard those ns2 project in New York plans that violate the latency constraints expressed in the view definition, using a simple analytical model that estimates the maximum latency of a given plan .Choose the plan from ns2 project in New York among the remaining plans that minimizes the monitoring perturbation, aspredicted by the analytical perturbation model Install a traced sensor ns2 project in New York in QueueManager in the queueing routine. This sensor generates an event record containing the value of the variable recording the queue size whenever a queue operation is ns2 project in New York invoked. Install a similar traced sensor in Queue– Manage.

     Both sensors send event records tothe ns2 project in New York resident monitor, with no queueing, which sendsthem to the central monitor, again without queueing.The action predicate is evaluated in the central monitor. If it is satisfied, the thisqueuesize attribute for the view is recorded in the main memory ns2 project in New York database, and a notification is sent to the proper process, without queueing. Install a traced sensor in Queuemanager that ns2 project in New York generates event records when the value of the variable recording the queue size transitions

Ns2 project in New Jersey

    Ns2 project in New Jersey analysis that is performed by an individual sensor, which is then termed an extended sensor, reduces the sensor’s degree of interaction with its resident monitor, thereby reducing monitoring overhead. For simple ns2 project in New Jersey analyses that are relatively inexpensive compared to the cost of communication, extended sensors may be preferred. More complex analysis must be performed ns2 project in New Jersey elsewhere, so that needless perturbation of the  process being monitored is avoided. A second tradeoff involves computation within the resident monitor.

      If the analysis is performed ns2 project in New Jersey within a resident monitor, its interactions with the ns2 project in New Jersey central monitor are reduced. However, excessive analysis within a specific resident monitor may lead to an undue computational load and process switching overhead ns2 project in New Jersey being imposed on the same processor on which the application processes being monitored are executing. This may not be tolerable for certain multiprocessor or ns2 project in New Jersey real-time architectures , as shown below. Additional tradeoffs concern the central monitor.

       If the central ns2 project in New Jersey monitor does not perform analysis and simply forwards unanalyzed data to the agent that requires the monitoring information excessive communication may result between central monitor and the “user.” However, the agent itself may ns2 project in New Jersey decide what analyses should be performed; it retains complete freedom regarding the questions that may be asked about the data being collected Altematively, such freedom may ns2 project in New Jersey be sacrificed by performing analysis within the central monitor, thereby reducing the degree of interaction with the “user.”

Ns2 project in United Arab Emirates

      Ns2 project in United Arab Emirates the location of the resident monitor process in relation to the application process(es), either on the same processor or on a dedicated processor in the same multiprocessor. The cost of event record generation in the application process. The ns2 project in United Arab Emirates communication cost between the application process and the resident monitor, and between the resident and central monitors, expressed as a fixed overhead plus the cost per byte of event records sent.

       The ns2 project in United Arab Emirates latency constraint of evaluating the action predicate, as expressed in the CORRECTclause of the view. The notification latency constraint, as expressed in the WITHINns2 project in United Arab Emirates portion of the NOTIFYclause. The relationship between program variables referenced the ns2 project in United Arab Emirates action predicate of the view, specifically, whether one object or multiple objects are involved, the process or processor co-residency  of objects involved, an ns2 project in United Arab Emirates estimate of the selectivity of subexpressions in the action predicate, and the approximate evaluation cost for the target list and action predicate.

      Toillustrate ns2 project in United Arab Emirates the manner in which these considerations affect the decisions made during sensor generation, consider the distributed monitoring system in, consisting of ns2 project in United Arab Emirates sensors, probes, and central and resident monitors. In this system, ns2 project in United Arab Emirates the analysis of data being collected may be performed either by individual sensors, by the resident monitor, by the central monitor, or by any ns2 project in United Arab Emirates combination thereof. Several implementation tradeoffs result.One tradeoff is monitoring overhead versus communication ns2 project in United Arab Emirates cost.

Ns2 project in Saudi Arabia

      Ns2 project in Saudi Arabia important aspects like perturbation\ and latency may be expressed as constraints, rather than procedurally. This implies that programmers need not understand the details of information collection and analysis, of monitoring system setup and distribution, etc. However, it also ns2 project in Saudi Arabia requires that such declarative specifications be automatically mapped to the low level collection ns2 project in Saudi Arabia  and evaluation mechanisms discussed in by the monitoring system’s compiler. Such mappings must ensure that the information collection and analysis ns2 project in Saudi Arabia meet possibly stringent real-time constraints, while minimally perturbing the application as it executes. Fortunately, mappings may be varied along several dimensions.

        This ns2 project in Saudi Arabia section will describe how the monitoring system’s compiler may determine appropriate mappings. Where should each subexpression of the action predicate and the expressions ns2 project in Saudi Arabia in the target list be performed: in the relevant sensor, in the application code, in the resident monitor, or in the central monitor, Should ns2 project in Saudi Arabia ns2 project in Saudi Arabia the sensor send event records to the resident monitor, or directly to the central monitor How long should event records be queued in the application process, and in the ns2 project in Saudi Arabia resident monitor How long should notifications be queued Should notifications be generated only in the central monitor, or also in the resident monitor, or even in the application program, We emphasize that these decisions are not independent, and that ns2 project in Saudi Arabia some alternatives are not available for all views.

      For instance, if the action predicate mentions two attributes associated with objects residing on ns2 project in Saudi Arabia different processors served by separate resident monitors, then the analysis must be done in the central monitor, as neither the sensors nor the resident monitors have sufficient information .

Ns2 project in Iraq

         Ns2 project in Iraq note that the analysis phase of monitoring often requires the comparison of time fields among multiple events that may have occurred on ns2 project in Iraq different nodes of the distributed system. We have not explored any novel methods for event or time synchronization . For most of our applications, it has been ns2 project in Iraq sufficient to assume that processor clocks are synchronized to within tens of microseconds. In conclusion, views as defined above are useful for specifying dynamic monitoring for several reasons: The real-time attributes of program monitoring, such as maximum monitoring ns2 project in Iraq delays, etc., are easily specified.

         Performance specifications regarding monitoring are easily stated, which results in the generation of efficient collection and analysis using probes, extended sensors, and analysis code in resident and central monitors. In essence, the monitor ns2 project in Iraq can tailor its collection and analysis mechanisms to single applications or even single execution runs of applications. Language and system independence are achieved by ns2 project in Iraq expressing views in terms of attributes rather than in terms of program variables present ns2 project in Iraq in the application.

       In addition, any program described with the E-R model may be monitored, including operating system components and systems software for a ns2 project in Iraq more extensive discussion of language issues in the specification of monitoring. The attachment of graphical representations to monitoring views is the subject of other ns2 project in Iraq past and future research performed by our group. It should be apparent from the in the previous section that the attribute and view languages permit users to express application-dependent monitoring views in a high level, declarative fashion.