Thanks a lot Christian for the well-explained documentation and this explains why I'm seeing the trouble with topic durable subscriptions regarding the per-destination memory usage & limit.
First, let me quote some from your writing: "Main Broker Memory, Destination Memory, Subscription Memory ... A destination, when it’s created, will create its own SystemUsage object (which creates its own separate Memory, Store, and Temp Usage objects) but it will set its parent to the be broker’s main SystemUsage object. A destination can have its memory limits tuned individually (but not Store and Temp, those will still delegate to the parent). To set a destination’s memory limit: ... So the destination usage objects can be used to more finely control MemoryUsage, but it will always coordinate with the Main memory for all usage counts. This functionality can be used to limit the number of messages that a destination keeps around so that a single destination cannot starve other destinations. *For queues, it also affects the store cursor’s high water mark. A queue has different cursors for persistent and non-persistent messages. If we hit the high water mark (a threshold of the destination’s memory limit), no more messages be cached ready to be dispatched, and non-persistent messages can be purged to temp disk as necessary (if the StoreCursor will use FilePendingMessageCursor… otherwise it will just use a VMPendingMessageCursor and won’t purge to temporary store).* If you don’t specify a memory limit for individual destinations, the destination’s SystemUsage will delegate to the parent (Main SystemUsage) for all usage counts. This means it will effectively use the broker’s Main SystemUsage for all memory-related counts. *Consumer subscriptions, on the other hand, don’t have any notion of their own SystemUsage or MemoryUsage counters. They will always use the broker’s Main SystemUsage objects.* The main thing to note about this is when using a FilePendingMessageCursor for subscriptions (for example, for a Topic subscription), the messages will not be swapped to disk until the cursor high-water mark (70% by default) is reached.. but that means 70% of Main memory will need to be reached. That could be a while, and a lot of messages could be kept in memory. And if your subscription is the one holding most of those messages, swapping to disk could take a while. As topics dispatch messages to one subscription at a time, if one subscription grinds to a halt because it’s swapping its messages to disk, the rest of the subscription ready to receive the message will also feel the slow down..." What I don't understand from the above is why consumer subscriptions (and their cursors) of topics are not using per-destination MemoryLimit but share the Broker's main MemoryLimit, unlike the queues (please see the bolded sentences above). Due to this + some logics inside AbstractStoreCursor's space checking logics, PFC always kicks in for the topic whenever the persistent store cursor's cache (pendingList) gets full. Let me explain what's happening: 1. A topic is created, with per-destination memory limit = 1MB and broker's main memory limit = 5MB. 2. Topic's SystemUsage (for PFC purpose) is configured with per-destination memory limit (1MB), while TopicStorePrefetch(persistent store cursor)'s SystemUsage (for remaining cache space checking purpose) is configured with broker's main memory limit (10MB). 3. The 1st message of 0.8MB is published: a. PFC doesn't kick in at Topic layer, as Topic#memoryUsage#isFull is true. b. It's cached to the persistent cursor, as AbstractStoreCursor#hasSpace is true. c. per-dest memory usage % becomes 90%, while main memory usage % becomes 9%. 4. The 2nd message of 0.8MB is published: a. PFC doesn't kick in either, as per-dest memory usage is 90% (< 100%). This is fine. b. *(I expect here that this second message shouldn't be cached to the cursor but invalidate it, but)this second message is also cached to the persistent cursor, as AbstractStoreCursor#hasSpace is still true: 9% < 70% (main memory usage high watermark)!!!* c. per-dest memory usage % becomes 180%, while main memory usage % becomes 18%. 5. The 3rd message of 0.8MB is published: a. *(I don't want this behavior but) PFC kicks in!!!* because per-destination memory limit is exceeded (180%). The behavior I wanted to see is: at #4.b. TopicStorePrefetch checks cursor memory availability against per-dest memory limit (not against broker's main memory limit) so that cursor pending cache gets disabled (just keeps what has been cached) w/o increasing the per-destination memory usage. I don't want to block persistent message publishing to topics by the per-destination memory limit but only for non-persistent message publishing, cause the store size allowed for a destination is relatively higher than the memory limit: e.g. I'd like to allow per-destination persistent message publishing up to 10GB disk space without being blocked by the memory limit & PFC... How can I achieve this? -- View this message in context: http://activemq.2283324.n4.nabble.com/cursor-memory-usage-limit-vs-memory-usage-limit-tp4669679p4669819.html Sent from the ActiveMQ - User mailing list archive at Nabble.com.
