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Performance TuningCompiled from:Oracle Database Administration,
Session 13, Performance, Harvard UOracle Server Tuning Accelerator,
David Scott, Intec
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Case Study #1Define the BUSINESS problemThe GUI is too slow; a
loss in productivity $$$Measure the painScreen XYZ in the GUI takes
47 seconds3000 users use this screen at each loginMost other
screens are fineIdentify the problem componentStopwatch timing of
XYZ response is 47 secondsSame SQL query takes 47 secondsQuery
identified as culprit
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Case Study #1 (contd)Find the root causeInefficient
queryInvestigate and weigh solutionsMultiple versions of query
comparedResults must match originalFix the problemReplace query in
Screen XYZ with tuned versionMeasure the resultsQuery returns in 2
secondsROI: 3000 users * 45 seconds saved * Avg salary @ $10/hour *
260 business days/year = $97,500
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Performance TuningTrade-offs Between Response Time and
ThroughputGoals for tuning vary, depending on the needs of the
applicationOLTP vs. OLAP applications (which one requires which
performance?)
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Performance DefinitionResponse time = service time + wait timeWe
can increase performance two ways: by reducing service time by
reducing wait time
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Performance DefinitionSystem throughput equals the amount of
work accomplished in a given amount of timeTwo techniques of
increasing throughput existGet more work done with the same
resources (reduce service time)Get the work done quicker by
reducing overall response time (reduce wait time)
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Performance DefinitionThe service time for a task may stay the
same, but wait time increases as contention increasesIf many users
are waiting for a service that takes 1 second, then the tenth user
must wait 9 seconds for a service that takes 1 second
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Wheres the Wait?Client ApplicationNetworkDisk
CPUDatabase
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Critical ResourcesResources such as CPUs, memory, I/O capacity,
and network bandwidth are key to reducing service timeAdding
resources can give higher throughput and swifter response times
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SQL Processing Architecture
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ParserThe parser performs two functions:Syntax analysis: This
checks SQL statements for correct syntaxSemantic analysis: Checks
that the current database objects and object attributes are
correct
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OptimizerThe optimizer is the heart of the SQL processing
engine. The Oracle server provides two methods of optimization:
rule-based optimizer (RBO) and cost-based optimizer (CBO).Note: As
of Oracle 10g, RBO is no longer supported.
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Row Source GeneratorThe row source generator receives the
optimal plan from the optimizerIt outputs the execution plan for
the SQL statement A set of rows returned by an execution step is
called a row sourceThe execution plan is a collection of row
sources, structured in the form of a tree
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SQL ExecutionThe combination of steps required to execute a
statement is called an execution planAn execution plan includes an
access method for each table that the statement accesses and an
ordering of the tables (the join order)
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Example 1How will the following SQL statement be
processed?SELECT *FROM BLLIM.Project;
Does it matter if an index exists?
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Example 2How will the following SQL statement be
processed?SELECT *FROM BLLIM.ProjectWHERE status = C; // C for
complete
Does it matter if an index exists?
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Example 3How will the following SQL statement be
processed?SELECT *FROM BLLIM.ProjectWHERE status = C; // C for
complete
Does it matter if an index exists?What if the distribution of
status is the following (skewed)?70 projects have C, 10 have I, and
20 have A
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Example 4How will the following SQL statement be
processed?SELECT pjTitleFROM BLLIM.ProjectWHERE status = C; // C
for complete
Does it matter if an index exists?Assume that you have an index
for status and another one for pjTitle.
