Latch, mutex and beyond

April 12, 2010

Latch get “where” and “why”.

Filed under: Uncategorized — andreynikolaev @ 7:48 pm

It is widely known that the Oracle server uses kslgetlKernel Service Lock Management Get Latch function to acquire the latch. In 2006 Tanel Poder first demonstrated that  oradebug call  kslgetl/kslfre can be used to acquire the latch manually. This is very useful  to simulate latch related hangs and contention.

For several years it was commonly supposed that kslgetl() has two parameters – latch address and wait. But on AIX 5L we have unique procstack tool. This tool shows the actual number of parameters for function. It occurs that kslgetl has four parameters:

...
sskgpwwait(??, ??, ??, ??, ??) + 0x38
skgpwwait(??, ??, ??, ??, ??) + 0xbc
kslges(??, ??, ??, ??, ??) + 0x54c
kslgetl(??, ??, ??, ??) + 0x33c
ksfglt(??, ??, ??, ??, ??) + 0x198
...


We do know the meaning the first two of parameters. What about the others? (more…)

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