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TNS:could not resolve the connect identifier specified
Backtrace message unwound by exceptions
invalid identifier
PL/SQL compilation error
internal error
missing expression
table or view does not exist
end-of-file on communication channel
TNS:listener unknown in connect descriptor
insufficient privileges
PL/SQL: numeric or value error string
TNS:protocol adapter error
ORACLE not available
target host or object does not exist
invalid number
unable to allocate string bytes of shared memory
resource busy and acquire with NOWAIT specified
error occurred at recursive SQL level string
ORACLE initialization or shutdown in progress
archiver error. Connect internal only, until freed
snapshot too old
unable to extend temp segment by string in tablespace
Credential retrieval failed
missing or invalid option
invalid username/password; logon denied
unable to create INITIAL extent for segment
out of process memory when trying to allocate string bytes
shared memory realm does not exist
cannot insert NULL
TNS:unable to connect to destination
remote database not found ora-02019
exception encountered: core dump
inconsistent datatypes
no data found
TNS:operation timed out
PL/SQL: could not find program
existing state of packages has been discarded
maximum number of processes exceeded
error signaled in parallel query server
ORACLE instance terminated. Disconnection forced
TNS:packet writer failure
see ORA-12699
missing right parenthesis
name is already used by an existing object
cannot identify/lock data file
invalid file operation
quoted string not properly terminated

RE: difference between child and parent latches?

Tanel Poder

2004-03-22

Replies:
> Not quite true. (at least starting from 9i). The shared pool is
> divided
> in to multiple sub-pools if it is greater than 250MB and/or if your
> cpu_count > 4. In this case the shared pool is covered by multiple
> shared pool latches.

I use my chance here to throw in an undocumented parameter _kghdsidx_count, which you could modify to manually control into how many heaps shared pool will be divided.

Each heap has it's own freelist and lru lists and the latch protecting operations on them, this means you could relieve shared pool latch contention in extremely poorly written applications, but also you might introduce unnecessary ORA-4031 problems, when most allocations happen to be non-uniformly distributed to some specific heap resulting in out of memory error, while others heaps have might have enough (but unusable) space in them..

About parent vs child latches. There is no fundamental low level difference between parent and child latches, they are all small regions of memory modified with atomic test-and-set style opcodes.

You see parent (and solitary) latches from x$ksllt where kslltcnm = 0 and child latches have kslltcnm > 0 (their child number is stored there).

V$LATCH_PARENT shows all latches with kslltcnm 0, V$LATCH_CHILDREN shows all latches with cnm > 0. V$LATCH just summarizes & groups all statistics up using the latch number, it doesn't care about parent vs child latches.

It's up to Oracle, how it uses the child and parent latches, normally when child latches are used, parent latches don't get used much (or at all), since all resources to be protected have been spread between child latches already.

However, there is a case with library cache parent latch (as mentioned also in Steve Adams book), it doesn't get used normally, but when you flush the shared pool, it get's used for example.


Tanel.