ns2 project in berlin

      ns2 project in berlin thus, it is difficult to see how lazy matching can be folded into the object level match phase, or whether it is ns2 project in berlin desirable at all. The metarule matching method that one adopts is influenced by the considerations cited above. In the rest of this paper, we attempt to enumerate specific feasible techniques ns2 project in berlin and briefly outline their characteristics.- The first technique consists of compiling metarules into the object level matcher. This means that if one is using a RETE or TREAT ns2 project in berlin discrimination net matcher, for example, one can compile the metarule tests into the network.

     At the network nodes where final instance tokens are generated, one can insert ns2 project in berlin  additional test nodes, compiled from the metarules, and thus inhibit certain instances ns2 project in berlin from proceeding onward to the firing mechanism, i.e., redact them. This is practical when considering main memory based systems. Instances can simply be treated like any other token in this case If aggregate metarules are supported, however, we have several ns2 project in berlin problems. First, the network nodes storing instance tokens will likely grow very large especially when computing aggregate metarules. The performance of memory ns2 project ns2 project in berlin in berlin based systems would degrade significantly.

    Second an ‘Laggregate condition” to be tested at these nodes will have to be inhibited until all instances have been ns2 project in berlin computed. Thus, some means of determining when the match is completed and all instances have been computed is needed. This approach is essentially the same as the one proposed in. Now let’s consider base metarules for a moment in this context. The approach ns2 project in berlin is very straight.forward.

Ns2 project in Idaho

      Ns2 project in Idaho next, consider a different global event, which permits the system to use extended sensors for the event’s analysis. If the global event is then an extended sensor will generate events for the resident monitor only if its attribute’s ns2 project in Idaho respective value is , thereby reducing the total number of event records generated by the process This sensorbased analysis results in the lowest perturbation reported in the table above .

      Further ns 2project in Idaho reductions in perturbation may be achieved in several ways, including theuse of shared memory among user processes and the resident monitor to share ns2 project in Idaho monitoring information  the use of threads versus processes for representation of resident monitors , or the delivery of monitoring information across additional communication ns2 project in Idaho links among workstations, much like with the monitoring hardware additions in the Intel Paragom machine. In conclusion, the measurements reported in the table area simple illustration of the heuristic mentioned above: in the network ns2 project in Idaho environment, analysis should be moved as close to collection as possible.

     Note that this observation holds in computer networks, multicomputers  and multiprocessors, as long as the communication ns2 project in Idaho costs significantly outweigh the costs of the analysis being performed. We conjecture that this result will also hold for the monitoring hardware provided with the new Intel Paragom multicomputer, since its communication bandwidths are significantly lessthat the ns2project in Idaho computational power of the Intelused as a communication co-processor.An implementation of the monitor on a real-time multiprocessor system ns2 project in Idaho exhibits differences in several basic system parameters and therefore, dictates the use of different heuristics.

Ns2 project in manchester

     Ns2 project in Manchester at each event time, the process may elect to generate or not generate on actual event, where the generated event is an assignment of the value or  to ns2 project in Manchester a local variable mapped to a monitoring attributein the process  The global event to the evaluated by the monitoring system   The global event’s frequency of change for each program run is not known due to the randomness of the individual ns2 project in manchester event generators. In the measurements below, generator processes are first run without monitoring and then the event of interest is analyzed with extended sensors, by the resident monitor, or by the central monitor, respectively, each time measuring the ns2 project in Manchester resulting program perturbation.

       The table below depicts the measurement results In all cases above, the actual overhead reported here is dominated by the use of Unix communication ns2 project in Manchester primitives. Thus, the exact amounts of the reported overhead percentages is not relevant. Instead, observe the differences in the amounts reported above. Specifically, ns2 project in Manchester the entry “Unmonitored” depicts the total time in seconds for the unmonitored execution of two generating processes located on the same machine. The entry “Central” assumes ns2 project in Manchester the generation of event records by generator processes each time an actual assignment to attributel or attribute is performed.

      Those event ns2 project in Manchester records are then sent to the nonlocal central monitor  which compares the values of the respective attributes. Compared to the measurements in row “Central,” it is apparent that a comparison of attribute values using a resident monitor on the generators’ workstation is preferable to central monitoring This result holds despite the additional cost of context ns2 project in Manchester switching caused by the execution of the resident monitor on the generator processes’ workstation.

Ns2 project in liverpool

      Ns2 project in Liverpool while the full four-step process presented in the previous section may be automated, it can be be simplified significantly ns2 project in liverpool for particular hardware and software configurations. Inthis section, we present the plan simplifications used for the three hardware configurations on which the monitor has ns2 project in Liverpool been implementedThe first configuration is a local area network containing Sun  machines and a Pyramid communicating over an Ethernet . Asdiscussed in, communication in such an environment is very expensive compared with processing time. Hence, ns2 project in Liverpool for this configuration, we apply the following heuristic: push analyses to the lowest level where they may be performed, thereby reducing communication as much ns2 project in Liverpool as possible.

       This decision is motivated by the experimental results presented next, and is justified elsewhere Inparticular, this heuristic can be shown to minimize perturbation ns2 project in Liverpool and latency simultaneously for this configuration with all but artificially complex view specifications. This heuristic ensures that analyses of monitoring ns2 project in Liverpool information possible within the same address space in which the required sensors are located will be performed locally.

      A resident monitor performs the analysis that ns2 project in Liverpool requires event records collected from different processes on its node, and the central monitor performs the analysis that requires event records from multiple machines. The experimental results regarding the perturbation experienced in the distributed implementation of the monitoring system described next rely on a distributed workload generator. In the experiment below, the generator’s configuration consists of two event generator processes, both of which are collocated on a single Sun workstation. A resident monitor is also ns2 project in liverpool located on the workstation, but the central monitor resides on a different workstation on the same subnet. Each event generator process generates up to randomly drawn events.

 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