[jira] Commented: (JCR-2786) Cluster sync not always done when calling session.refresh(..)
[ https://issues.apache.org/jira/browse/JCR-2786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921378#action_12921378 ] Thomas Mueller commented on JCR-2786: - The easiest solution is to call syncCount++ before calling journal.sync(), but I will also replace the volatile syncCount with AtomicInteger. > Cluster sync not always done when calling session.refresh(..) > - > > Key: JCR-2786 > URL: https://issues.apache.org/jira/browse/JCR-2786 > Project: Jackrabbit Content Repository > Issue Type: Bug > Components: clustering >Reporter: Thomas Mueller >Assignee: Thomas Mueller > > Session.refresh(..) is supposed to synchronize cluster changes, but this > doesn't always happen, specially if the syncDelay is low. The reason is a > wrong assumption in ClusterNode.sync: The code there to avoid duplicate sync > calls doesn't always work as expected. The following algorithm is used: > int count = syncCount; > syncLock.acquire(); > if (count == syncCount) { > journalSync(); > syncCount++; > } > syncLock.release(); > The problem is that the background thread might be at the line "syncCount++" > when Session.refresh(..) is called, so that the main thread believes > journalSync was already called and thus doesn't call it. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.
[jira] Commented: (JCR-2786) Cluster sync not always done when calling session.refresh(..)
[ https://issues.apache.org/jira/browse/JCR-2786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921389#action_12921389 ] Jukka Zitting commented on JCR-2786: Moving the syncCount increment before the sync() call can cause unnecessary cluster syncs when multiple sessions are refreshed concurrently. > Cluster sync not always done when calling session.refresh(..) > - > > Key: JCR-2786 > URL: https://issues.apache.org/jira/browse/JCR-2786 > Project: Jackrabbit Content Repository > Issue Type: Bug > Components: clustering >Reporter: Thomas Mueller >Assignee: Thomas Mueller > > Session.refresh(..) is supposed to synchronize cluster changes, but this > doesn't always happen, specially if the syncDelay is low. The reason is a > wrong assumption in ClusterNode.sync: The code there to avoid duplicate sync > calls doesn't always work as expected. The following algorithm is used: > int count = syncCount; > syncLock.acquire(); > if (count == syncCount) { > journalSync(); > syncCount++; > } > syncLock.release(); > The problem is that the background thread might be at the line "syncCount++" > when Session.refresh(..) is called, so that the main thread believes > journalSync was already called and thus doesn't call it. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.
[jira] Commented: (JCR-2786) Cluster sync not always done when calling session.refresh(..)
[ https://issues.apache.org/jira/browse/JCR-2786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921395#action_12921395 ] Thomas Mueller commented on JCR-2786: - Hi Jukka - what do you suggest? Having some way to enforce a cluster sync is nice; in my view it doesn't need to be Session.refresh(..). > Cluster sync not always done when calling session.refresh(..) > - > > Key: JCR-2786 > URL: https://issues.apache.org/jira/browse/JCR-2786 > Project: Jackrabbit Content Repository > Issue Type: Bug > Components: clustering >Reporter: Thomas Mueller >Assignee: Thomas Mueller > > Session.refresh(..) is supposed to synchronize cluster changes, but this > doesn't always happen, specially if the syncDelay is low. The reason is a > wrong assumption in ClusterNode.sync: The code there to avoid duplicate sync > calls doesn't always work as expected. The following algorithm is used: > int count = syncCount; > syncLock.acquire(); > if (count == syncCount) { > journalSync(); > syncCount++; > } > syncLock.release(); > The problem is that the background thread might be at the line "syncCount++" > when Session.refresh(..) is called, so that the main thread believes > journalSync was already called and thus doesn't call it. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.
[jira] Commented: (JCR-2786) Cluster sync not always done when calling session.refresh(..)
[ https://issues.apache.org/jira/browse/JCR-2786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12921410#action_12921410 ] Jukka Zitting commented on JCR-2786: My original thinking behind the syncCount mechanism from JCR-1753 was to skip the cluster sync if another thread completes the sync after the sync() method was entered. I missed the case where a thread performs the sync but is then delayed before it gets to the syncCount++ statement. Your fix changes the logic from checking whether a sync was completed to whether a sync was *started* after the sync() method was entered, which raises the likelihood of extra cluster syncs. However, of the top of my head I don't see any good way to reliably track the completion of a cluster sync, so for now I think your solution is the best. At least it can only causes one extra cluster sync even if n threads were blocked waiting on syncLock. PS: AtomicInteger enables a more elegant way to implement the check-and-increment operation: if (count == syncCount.get()) { syncCount.incrementAndGet(); ... } vs. if (syncCount.compareAndSet(count, count + 1)) { ...; } > Cluster sync not always done when calling session.refresh(..) > - > > Key: JCR-2786 > URL: https://issues.apache.org/jira/browse/JCR-2786 > Project: Jackrabbit Content Repository > Issue Type: Bug > Components: clustering >Reporter: Thomas Mueller >Assignee: Thomas Mueller > > Session.refresh(..) is supposed to synchronize cluster changes, but this > doesn't always happen, specially if the syncDelay is low. The reason is a > wrong assumption in ClusterNode.sync: The code there to avoid duplicate sync > calls doesn't always work as expected. The following algorithm is used: > int count = syncCount; > syncLock.acquire(); > if (count == syncCount) { > journalSync(); > syncCount++; > } > syncLock.release(); > The problem is that the background thread might be at the line "syncCount++" > when Session.refresh(..) is called, so that the main thread believes > journalSync was already called and thus doesn't call it. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.