In-memory replication and no. of sessions - clarification

Question

          a small question/clarification
          Lets say we have 2 servers in cluster with in-memory repication. Let say maximum RAM for jvm heap can use is 1.5GB.
          I understand that HTTP Session Data is stored in heap (am i wrong?).
          Now lets say if we set weblogic.httpd.session.cacheEntries=1024 (default).
          The documentation says...
          weblogic.httpd.session.cacheEntries=x
          Where x limits the number of cached sessions at any time. If you are expecting high volumes of simultaneous active sessions, you do not want these sessions to soak up the RAM of your server since this may cause performance problems swapping to and from virtual memory. When the cache is full, the least recently used sessions are stored in the persistent store and recalled automatically when required. If you do not use persistence, this property is ignored, and there is no soft limit to the number of sessions allowed in main memory. By default, the number of cached sessions is 1024. The minimum is 16, and maximum is Integer.MAX_VALUE. An empty session uses less than 100 bytes, but will grow as data is added to it.
          If lets say 1025 user comes in what happens in followin scenario
          1. no heap memory available:
          Does is throw out of memory exception or what does it do to accomodate new user?
          Does swapping occur for HTTP data on the heap? (or am i talking nonsense?)
          2. heap memory available:
          What does the following mean for in-memory replication?
          When the cache is full, the least recently used sessions are stored in the persistent store and recalled automatically when required.
          thanks in advance
          

Answer 1

shivu wrote:
          > a small question/clarification
          >
          > Lets say we have 2 servers in cluster with in-memory repication. Let say maximum RAM for jvm heap can use is 1.5GB.
          Dont' allocate 1GB for heap. Try not to allocate more than 512 MB.
          > I understand that HTTP Session Data is stored in heap (am i wrong?).
          >
          > Now lets say if we set weblogic.httpd.session.cacheEntries=1024 (default).
          >
          > The documentation says...
          > -----------
          > weblogic.httpd.session.cacheEntries=x
          > Where x limits the number of cached sessions at any time. If you are expecting high volumes of simultaneous active sessions, you do not want these sessions to soak up the RAM of your server since this may cause performance problems swapping to and from virtual memory. When the cache is full, the least recently used sessions are stored in the persistent store and recalled automatically when required. If you do not use persistence, this property is ignored, and there is no soft limit to the number of sessions allowed in main memory. By default, the number of cached sessions is 1024. The minimum is 16, and maximum is Integer.MAX_VALUE. An empty session uses less than 100 bytes, but will grow as data is added to it.
          > ------------
          >
          > If lets say 1025 user comes in what happens in followin scenario
          >
          > 1. no heap memory available:Does is throw out of memory exception or what does it do to accomodate new user?
          > Does swapping occur for HTTP data on the heap? (or am i talking nonsense?)
          If you are out of memory you are out of luck.
          >
          > 2. heap memory available:
          >
          > What does the following mean for in-memory replication?
          > -----
          > When the cache is full, the least recently used sessions are stored in the persistent store and recalled automatically when required.
          > ----
          Hmm. I don't think there is any hard limit with in memory replication. But I would check and let you know.
          >
          > thanks in advance
          Cheers
          - Prasad