I ran some testing by injecting printline statements after the beginning of each synchronization block in all of the xwiki codebase and then ran some tests.
xwiki webstandards test: pages loaded: 925 synchronization blocks entered: 2,512,524 synchronizations per page: 2,716 Excluding the first page load on start-up, these are the total synchronizations from running the webstandards tests. Note that they don't add up to exactly 2,512,524 because some were spoiled when 2 threads tried to write to stdout simultaneously. Total Percent Location 1651401 65.73% XWikiCacheStore.java:115 316411 12.59% EmbeddableComponentManager.java:352 142094 5.66% XWikiContext.java:260 103028 4.10% XWiki.java:5380 58151 2.31% XWikiContext.java:282 54891 2.18% XWiki.java:5455 46324 1.84% DefaultVelocityFactory.java:72 46320 1.84% DefaultVelocityFactory.java:82 29447 1.17% EmbeddableComponentManager.java:138 15010 0.60% DefaultBeanManager.java:204 14595 0.58% DefaultXWikiRenderingEngine.java:239 10933 0.44% URIClassLoader.java:438 3812 0.15% XWiki.java:5406 3262 0.13% DefaultVelocityEngine.java:227 3262 0.13% DefaultVelocityEngine.java:245 2867 0.11% XWikiNotificationManager.java:130 1941 0.08% XWikiGroupServiceImpl.java:798 958 0.04% XWikiConfigurationService.java:50 958 0.04% XWikiNotificationManager.java:254 958 0.04% XWikiNotificationManager.java:265 957 0.04% XWikiCacheStore.java:704 951 0.04% XWikiNotificationManager.java:230 949 0.04% XWikiNotificationManager.java:241 917 0.04% XWikiNotificationManager.java:219 852 0.03% XWikiStatsServiceImpl.java:182 371 0.01% XWikiDocumentQueue.java:88 351 0.01% XWikiDocumentQueue.java:55 142 0.01% XWikiDocumentQueue.java:69 112 0.00% XWikiDocumentQueue.java:98 66 0.00% AdminAction.java:57 24 0.00% RightsManager.java:164 15 0.00% EditAction.java:59 UI tests were also run to give a more well rounded view of what real traffic might look like: 1666727 57.98% XWikiCacheStore.java:115 463369 16.12% EmbeddableComponentManager.java:352 234027 8.14% XWiki.java:5380 175972 6.12% XWikiContext.java:260 70156 2.44% XWikiContext.java:282 65952 2.29% XWiki.java:5455 43553 1.52% DefaultVelocityFactory.java:72 43552 1.52% DefaultVelocityFactory.java:82 33512 1.17% EmbeddableComponentManager.java:138 13451 0.47% DefaultBeanManager.java:204 9650 0.34% DefaultXWikiRenderingEngine.java:239 9450 0.33% XWikiNotificationManager.java:130 5176 0.18% XWikiGroupServiceImpl.java:798 5019 0.17% URIClassLoader.java:438 3965 0.14% XWiki.java:5406 2850 0.10% DefaultVelocityEngine.java:227 2850 0.10% DefaultVelocityEngine.java:245 2717 0.09% XWikiConfigurationService.java:50 2694 0.09% XWikiCacheStore.java:704 2624 0.09% XWikiNotificationManager.java:219 2624 0.09% XWikiNotificationManager.java:230 2624 0.09% XWikiNotificationManager.java:241 2590 0.09% XWikiNotificationManager.java:254 2590 0.09% XWikiNotificationManager.java:265 749 0.03% XWikiDocumentQueue.java:69 718 0.02% XWikiStatsServiceImpl.java:182 554 0.02% XWikiDocumentQueue.java:88 550 0.02% EmbeddableComponentManager.java:201 476 0.02% XWikiDocumentQueue.java:55 406 0.01% XWikiHibernateVersioningStore.java:142 403 0.01% XWikiNotificationManager.java:140 403 0.01% XWikiNotificationManager.java:155 403 0.01% XWikiNotificationManager.java:167 403 0.01% XWikiNotificationManager.java:181 403 0.01% XWikiNotificationManager.java:194 403 0.01% XWikiNotificationManager.java:206 282 0.01% XWikiDocumentQueue.java:98 209 0.01% EditAction.java:59 101 0.00% RightsManager.java:164 81 0.00% AdminAction.java:57 61 0.00% EmbeddableComponentManager.java:289 52 0.00% EmbeddableComponentManager.java:256 44 0.00% LucenePlugin.java:656 35 0.00% InlineAction.java:39 23 0.00% DefaultCSRFToken.java:130 19 0.00% MutableHttpServletRequestFactory.java:43 15 0.00% AbstractGenericComponentManager.java:93 13 0.00% LucenePlugin.java:450 5 0.00% XWikiNotificationManager.java:56 2 0.00% MacroRepository.java:65 2 0.00% XWiki.java:408 1 0.00% ActivityStreamCleaner.java:89 1 0.00% EmbeddableComponentManager.java:163 1 0.00% EmbeddableComponentManager.java:269 1 0.00% RightsManagerListener.java:85 1 0.00% SchedulerPlugin.java:561 1 0.00% StackingComponentEventManager.java:69 1 0.00% XWikiGroupServiceImpl.java:150 1 0.00% XWikiGroupServiceImpl.java:162 1 0.00% XWikiGroupServiceImpl.java:180 1 0.00% XWikiHibernateBaseStore.java:142 1 0.00% XWikiHibernateBaseStore.java:265 1 0.00% XWikiHibernateBaseStore.java:557 1 0.00% XWiki.java:5493 1 0.00% XWiki.java:5515 These numbers seem to be quite conclusive that XWikiCacheStore.java:115 is the lowest hanging fruit in the synchronization field. An examination of XWikiCacheStore reveals that the "per load" synchronization should be avoidable if it is not lazy initialized and is flushed differently. Is synchronization the best place to attack for performance gains? Synchronization cost is difficult to measure because it varies based on number of processor cores and processor sockets. In the worst case, the caches in multiple cores on multiple processor sockets all need to be flushed and this would be the case with high contention mutexes. As a matter of good practice, I think we should reduce the amount of synchronization as much as is reasonable. Caleb _______________________________________________ devs mailing list [email protected] http://lists.xwiki.org/mailman/listinfo/devs
