Database Reference
In-Depth Information
Polling
Active request for a resource in a tight loop.
Polling
is often responsible for large amounts of
wasted CPU time. Whenever possible, processes should be
sleeping
while waiting for a
resource instead of actively polling for a resource's availability.
POSIX
POSIX
(Portable Operating System Interface) is the collective name of a family of related
standards, which define the application programming interface (API) for software compat-
ible with variants of the UNIX operating system.
Random access memory (RAM)
Random access memory
is the volatile main memory of a computer system.
Real Application Clusters (RAC)
Multi-instance variant of the ORACLE DBMS that runs on clustered hardware to achieve
scalability and high availability. RAC requires cluster software, such as Oracle Clusterware,
HP-UX ServiceGuard, IBM HACMP, Veritas Cluster, Sun Cluster, or HP TruCluster.
Recursive SQL
SQL statements the ORACLE DBMS executes against the data dictionary as user SYS in order
to service a request from a database client. See also
user level SQL
.
Resource profile
An apportionment of response time often presented in tabular form. Each row of a tabular
resource profile
contains a single contributor to response time, for example CPU time consump-
tion or a
wait event
. Ideally, the following columns are included: contributor name, percentage
of response time, contribution to response time in seconds, number of times the contributor
was called upon, and average time consumed by a call upon the contributor. The table
should be sorted by percentage of contribution to response time in descending order.
Response time
The wall clock time an electronic system needs to fulfill a request by a user. Response time
consists of CPU time consumption and waiting.
Rule-based SQL optimizer (RBO)
The
rule-based SQL optimizer
was the simpler predecessor of the more advanced
cost
based
SQL optimizer
(CBO). The RBO generated execution plans based on a fixed set of rules. It
knew nothing about table sizes and column selectivities. The RBO is obsolete since the
release of Oracle10
g
.
