Database Reference
In-Depth Information
End-to-end metrics
The term end-to-end metrics refers to the ability of the ORACLE DBMS to provide metrics
based on
application instrumentation
.
Enqueue
An
enqueue
is a locking mechanism that queues up requestors and services them in a first-
in-first-out (FIFO) order. Enqueues may be acquired in different modes, such as exclusive
and shared.
Execute
Execution of a SQL statement or PL/SQL block. Performs the operation coded by a DDL or
DML statement. For
SELECT
statements, places the cursor on the first row of the result set.
Fetch
Data retrieval by a
SELECT
statement.
Idle wait
Interval of time during which no request is made upon an ORACLE server process. As the
user accumulates
think time
, the server accumulates idle wait time.
Instance (a.k.a. DBMS instance)
Collection of processes and memory structures that implement the ORACLE database server by
running the program
$ORACLE_HOME/bin/oracle
on UNIX or
%ORACLE_HOME%\bin\oracle.exe
on Windows.
Instance service name
Instance service names
are the service names an instance registers with one or more TNS
Listeners. They are set with the initialization parameter
SERVICE_NAMES
. In Oracle10
g
, the
package
DBMS_SERVICE
may be used to add instance services. The
SERVICE_NAME
setting in the
body of a
Net service name
definition references an instance service name.
Instrumentation
Program code in some computer language that allows the program to measure itself and to
record how much time it spends per program module.
Latch
Synchronization mechanism used by the ORACLE server to implement mutual exclusion for
critical sections of program code to keep data structures consistent, by allowing only one
process at a time to enter the critical section. Processes consume CPU time (“spin”; the undoc-
umented parameter
_SPIN_COUNT
controls how many times) as they repeatedly attempt to
acquire a latch. Unlike
enqueues
, latches do not queue up requestors and have no other modes
except exclusive. Latches are implemented with atomic test-and-set machine instructions.
