Francesco Nigro created ARTEMIS-2746:
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Summary: Reduce memory footprint of journal loading
Key: ARTEMIS-2746
URL: https://issues.apache.org/jira/browse/ARTEMIS-2746
Project: ActiveMQ Artemis
Issue Type: Improvement
Components: Broker
Reporter: Francesco Nigro
While loading the journal, before reloading the messages into each queue, we
store the a reference to the message and some additional information
(scheduledDeliveryTime and deliveryCount) on a LinkedHashMap per-queue.
These information are using a AddMessageRecord class that can weigth 28 bytes:
12 object header + 4 for Message + 8 for scheduledDeliveryTime + 4
deliveryCount + 4 padding on a JDK 64 bits bits with COOPS.
Often both scheduledDeliveryTime and deliveryCount are not used, hence we could
save 12 bytes per-message by using a separate data-structure to hold such
additional records.
Such records could be stored in a separate LongObjectHasMap that would cost
approximately (it depends on the load factor) per-entry:
8 (for the messageID key) + 4 (for the additional record reference) + 16 (for
the record instance) = 28 bytes
In the worst case, given that the additional informations require the same
amount of memory (28 bytes), the only downside would be some lookup cost while
walking/updating both the data-structures, but in the best case (and most
common cases) it means eg
100_000 elements = saved ~2.8 MB
1_000_000 elements = saved ~28 MB
10_000_000 elements = saved ~280 MB
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