sap memory analyzer...basic steps and features walk-through ... objects or sizes > 2 gb. once...

© SAP AG 2007, Memory Analysis with SAP Memory Analyzer / 1

Welcome to the SAP Memory Analyzer

SAP Memory Analyzer: Basic Steps and Features Walk-through


Basic Steps with SAP Memory Analyzer

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(1) Get Heap Dump

(2) Parse Heap Dump

(3) Analyze Heap Dump


(1) Get Heap Dump

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Available for which JDKs?

• Sun, SAP and HP JDK• >= 1.4.2_12 and >= 1.5.0_7

Therefore applies to SAP:

• 640, 04s, 710, CE …• Windows, Solaris, HP-UX

HPROF Binary Heap Dump

Heap dump contains a snapshot of all objects that are alive at one point in time.

All ObjectsClass, fields, primitive values and

references

All ClassesClassLoader, name, super class, static

fields

All ClassLoadersDefined classes

Garbage Collection RootsObjects defined to be reachable by the JVM

IBM JDK has its own proprietary format.

You need to use IBM’s own tools.

How to get an heap dump?

• On Out Of Memory-XX:+HeapDumpOnOutOfMemoryError

• On Ctrl-Break-XX:+HeapDumpOnCtrlBreak

• AGENT LIB• JMAP• JCONSOLE• JVMMON


(2) Parse Heap Dump

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SAP Memory Analyzer parses heap dumps on first open. Preprocessing allows faster analysis on smaller machines.

64 bit machines only needed for dumps with > 20 million objects or sizes > 2 GB.

Once parsed, analyze the dump on 32 bit developer machines – it opens instantly.

A1SSize: S

98.000.000Objects



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Get an Overview

• total number of objects

• total heap size• class histogram

Identify HolderCheck ContentFind Big Chunks

Get Heap Dump

Parse Heap Dump

Analyze Heap Dump


(3) Analyze Heap Dump – Get an Overview

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Get an Overview




Snapshot Info and Class Histogram

Number of objects

Number of classes

Number of class loaders

The histogram lists per class the number of objects and their total shallow size. Anything but char[] is usually suspicious.

Total heap sizeLook out for accumulation of classes from the same package.


Class Histogram Grouping

Group classes by class loader

SAP Memory Analyzer extracts the names of the deployment units


(3) Analyze Heap Dump – Find Big Chunks

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Get an Overview



Find Big Chunks


Find Big Single Objects

Open the Dominator Treeto see the biggest distinct single objects Retained size = memory

freed if this object would be garbage collected

See Object Inspector for object details and field values.

This one HashMap keeps ~160MB alive, which are 6% of the total heap!

Look out for instances of the same class! Even better: group by classes (see next slide).


Find Big Groups of Objects

Group by classes to find big chunks kept alive by instances of one class

398 instances retain ~430MB, i.e. 15%!

4 classes in the .*sushi.*and .*sashimi.* packages consume 1.1 GB, i.e. 40%!


(3) Analyze Heap Dump – Check Content

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Get an Overview



Check ContentFind Big Chunks


Looking Into Big Memory Chunks

Drill down in the dominator tree: What is kept alive by the objects?

Using the context menu to show the histogram of the retained set, i.e. all objects kept alive grouped by classes.

Check outbound references to understand the data structures.


(3) Analyze Heap Dump – Identify Holder

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Get an Overview





Paths From GC Roots

The orange dot indicates a garbage collection root.

At the end of the line you see the reason, e.g. it could have been used as local variable.

For all GC Roots associated with a thread (Local Variable, Busy Monitor, JNI Local), we also show the thread.



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Get an Overview




Get Heap Dump

Parse Heap Dump

Analyze Heap Dump


Advanced Features

Execute SQL-like queries on the objects in the heap dump with the build-in OQL.

Use the console to run special purpose queries implemented in commands.


SAP NetWeaver FeaturesSAP Memory Analyzer extracts 640, NW04s and 710 sessions and displays domains, ids and size in one view.

The Cache view shows the content of all cache regions.


Groups of objectsFinding big chunks of memory

– Grouping in Dominator Tree– TOP_CONSUMERS– ARR_SZ_HISTOGRAM– LOCAL_VARS– OQL

Content Analysis– Object lists/histograms– Analyze the retained set– Class-level outbound references– OQL

Holder Analysis– Class-level inbound references– Multiple paths from the GC roots– Immediate Dominators

Single objectFinding big chunks of memory

– Check the Dominator Tree– TOP_CONSUMERS

Content Analysis– Expand/explore the Dominator Tree– Analyze the retained set– Object outbound references/Object inspector– OQL

Holder Analysis– Object inbound references– Paths from the GC roots

Feature Overview

Overview– Total heap size– Total number of objects/classes– Class histogram– Histogram by ClassLoader


Resources

SAP SDN Wiki

https://www.sdn.sap.com/irj/sdn/wiki?path=/display/Java/Java+Memory+Analysis

https://www.sdn.sap.com/irj/sdn/wiki?path=/display/Java/Java+Memory+Analysis

sap memory analyzer...basic steps and features walk-through ... objects or sizes > 2 gb. once...

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