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javagarbage-collectiong1gc
Igor Kiulian
Igor Kiulian

Reputation: 164

Java G1 Garbage collector takes a lot of memory

I have project with large database. To parse it I use java with G1 garbage collector. When program runs for a long period of time java begins to consume a lot of memory. But when I check java heap the size is much smaller. For example:

Question: what is taking the rest of my RAM? Is this overhead of G1?

Edit: Here is stats

RAM stats of my java procces: allocated ~50gb, consumed ~20gb

jmap info: heap size ~4gb

java procces: allocated ~50gb, consumed ~20gb
jmap info: heap size ~4gb

Upvotes: 3

Views: 2935

Answers (2)

Igor Kiulian
Igor Kiulian

Reputation: 164

I understood the problem. As @Holger mentioned the ram is allocated to java process but not fully filled with heap. But the reason why G1 allocates so many ram:

G1 suffers if it needs to allocate a lot of humongous regions. They will be created each time an object size > 50% of the region size. They will waste space as nothing else will be created in the region. Thus if its size is 51%, you will waste 49% of the region. Worse, if a region is 2MB and your object is 2.1MB, it will waste 1.9MB in the second region. If you allocate large objects, adjust your XX:G1HeapRegionSize.

Upvotes: 4

Anish
Anish

Reputation: 155

The RAM consumption will be because of the huge database size and the size of the result set.

Try the below: Optimizing Garbage Collection:

  • be wary of String Concatenation operator (+) use concat() instead

  • if using spring, try setFetchSize(number of rows to be fetched at a time) using setFetchSize will, however, increase your time for execution, but it is memory efficient

  • remove all unnecessary statement

  • Use Asynchronous Execution

Upvotes: 0

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