Details
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Wish
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Status: Open
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Minor
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Resolution: Unresolved
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0.1.0
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None
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None
Description
Tasks in TaskQueue and History are items that has to be "persisted" in a single crawl "session"/run. They are not consuming too much memory right now and this task is created for tracking some optimization ideas.
The following is some sample memory usage figures in a 32-bit Windows Vista environment: (refer to the attached test case)
- With javamex classmexer, 1M LinkTask in a queue consumes 280M of memory.
- For history, stores as MD5 as String, each URL could take 104 bytes only. 1M URL takes 100M roughly. (reference: http://www.javamex.com/tutorials/memory/string_memory_usage.shtml) Notice that MD5 is not guaranteed to be unique but it should be ok for general cases.
- To reduce memory footprint future, we may store MD5 as byte[], that take exactly 32 bytes, and will consumes 32M memory for 1M records
Previously, I ran a job that I try to reduce the memory usage for TaskQueue, I tried to simulate a Queue function with JBossCache that support eviction and passivation. JBossCache's passivation mechanism basically serialize the item into a database (or other device) and unload them from memory. It could effectively reduce memory usage. For a Queue with lots of items, there is no need to keep them all in memory as they won't be processed at the same time anyway. If it is necessary to keep a reference, we may passivate the LinkTask and just keep a hash (MD5, or even hashCode()).
There is one more way to store the tasks in an embedded database such as H2Database. It stores the data on disk.