Notes on the Oak Observation Queue

Deke Smith has written up a blog entry on JCR Observation here. JMX performance metrics on how the Jackrabbit Oak observation subsystem is performing can be obtained from /system/console/jmx (click on Oak Repository Statistics):

An explanation of these stats are available here.

During a single-threaded asset ingestion of JPG images, I observed the following (all values ‘per second’, with the highest value chosen):

SessionCount (number of active sessions) : 242
SessionReadCount (number of session read operations) : 12,557
SessionReadDuration (duration (nanoseconds) of session read operations) : 81,000,000
SessionReadAverage (average duration (nanoseconds) of session read operations) : 8,288
SessionWriteCount (number of session write operations) :1,438
SessionWriteDuration (duration (nanoseconds) of session write operations) : 203,000,000
SessionWriteAverage (average duration (nanosecondss) of session write operations) : 159,504
ObservationEventCount (Number of observation Event instances delivered) : 984
ObservationEventDuration (time (nanoseconds) spent processing observation events) : 12,637,302
ObservationEventAverage (average time (nanoseconds) spent processing observation events) : 14,530
ObservationQueueMaxLength : 6

According to Jackrabbit engineer Chetan Mehrotra - “…by default, the queue size is 1,000. If it crosses 1000, local events would be collapsed and converted to external events. If you have observation listeners marked to listen only for local changes, it would miss out on those events.”