Kevin Kempf's Blog

July 6, 2009

Automatic Shared Memory Management under 11i

Filed under: 11g, Oracle — Tags: — kkempf @ 1:04 pm

I’ve found it curious, watching my memory allocation (24 GB to the SGA) via Enterprise Manager for my ERP Production database (11g). In the past, under 32-bit Oracle RDBMS, it was always buffer cache hungry as it only had 3-4gb of SGA total (depending upon how many tricks you wanted to pull, you might eek out a little more or less.. glad those days are behind me!) Now, as you can see by the graph below, I watch as my buffer cache shrinks and my shared pool grows over time (31 days of history shown):

Memory Usage

I would be alarmed, except for 2 things. First, it seems to have stabilized at it’s current allocation for the last few days, and second, my buffer cache hit ratio is not suffering as a result (99.92% -> 99.89%):

Buffer Cache Hit Ratio

It almost feels like I have a memory leak in the shared pool somewhere, but this is the longest I’ve ever run my database under 11g (about 90 days of uptime) so I don’t know where it would normally “stabilize” to. At any rate, I swear under 10g it was closer to 80%/20% buffer cache to shared pool, and now its more like 45%/55% buffer cache to shared pool.


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