franz1981 commented on a change in pull request #2494: ARTEMIS-2224 Reduce
contention on LivePageCacheImpl
URL: https://github.com/apache/activemq-artemis/pull/2494#discussion_r246602031
##########
File path:
artemis-server/src/main/java/org/apache/activemq/artemis/core/paging/cursor/impl/LivePageCacheImpl.java
##########
@@ -48,54 +82,228 @@ public long getPageId() {
}
@Override
- public synchronized int getNumberOfMessages() {
- return messages.size();
+ public int getNumberOfMessages() {
+ while (true) {
+ final long size = producerIndex;
+ if (size == RESIZING) {
+ Thread.yield();
+ continue;
+ }
+ return (int) Math.min(size, Integer.MAX_VALUE);
+ }
}
@Override
- public synchronized void setMessages(PagedMessage[] messages) {
+ public void setMessages(PagedMessage[] messages) {
// This method shouldn't be called on liveCache, but we will provide the
implementation for it anyway
for (PagedMessage msg : messages) {
addLiveMessage(msg);
}
}
@Override
- public synchronized PagedMessage getMessage(int messageNumber) {
- if (messageNumber < messages.size()) {
- return messages.get(messageNumber);
- } else {
+ public PagedMessage getMessage(int messageNumber) {
+ if (messageNumber < 0) {
return null;
}
+ //it allow to perform less cache invalidations vs producerIndex if there
are bursts of appends
+ long size = lastSeenProducerIndex;
+ if (messageNumber >= size) {
+ while ((size = producerIndex) == RESIZING) {
+ Thread.yield();
+ }
+ //it is a message over the current size?
+ if (messageNumber >= size) {
Review comment:
Is not that easy here, this one is not a common collection (in theory, but
we can get an agreement on the contract for sure): it is more an append only
list that allows indexed queries like a map. In addition, is concurrent so if
you try to query something that's not in the collection in that moment, but you
will do it right after, there is a chance that you can get it if it has been
added in parallel by another thread.
If I remember correctly it is similar to an [hashed array
tree](https://en.wikipedia.org/wiki/Hashed_array_tree), where the top-level
directory is a double linked list of "folders" (instead of an array, like the
original implementation): indeed in the code there are chunkIndex (==key of top
level directory) and offset (==key of leaf into a directory).
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