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Navigation: Examples

Reducing data in the display

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Finding the signal in the noise

When you have a lot of data, it can be difficult to see the data that really matters - the signal within the noise.

This is especially the case when looking for a specific leak, rather than looking for all leaks.

There are a number of ways to reduce the amount of data:

•reduce the data collected

•reduce the data that is displayed

•filtering the data that is displayed

•use watermarks to display data between two points

Reducing collected data

Collected data can be controlled at different levels of granularity via the settings dialog.

Some settings pages can be used for fine tuning of how the data is collected and which hooks are enabled.

The collect tab allows quite coarse control over which types of hook are installed in the target program.

Settings menu instructionStep Edit Settings... Data Collection Collect page

Reducing displayed data

Data that ends up being collected can be removed from the display.

Most of the main tabs have a Display button to control what's shown:

•Memory

•Types

•Sizes

•Locations

•Generations

•Ages

•Hotspots

•Analysis

Filtered Data

Filters operate by matching source file and line number, callstack and datatype to keep or remove data.

A combination of permanent and temporary filters can be used, as well as global, session and local filters.

Watermarks

Watermarks let you not only add markers where certain events happened, but also let you display only the data for allocation events that happened between those watermarks.

The example usage of watermarks demonstrates this at the end

Example of reducing data in the display

Here's a simple example of reducing displayed data via the display settings dialog:

mvMemVal

launch nativeExample.exe instructionStep wait until attaching is complete

mvExample1

File menu instructionStep Exit

mvMemVal

wait for data transfer to complete

•Memory tab instructionStep Refresh shows the usual leaks and also memory errors

Roughly half the data is shown here:

example-reducing-data-more-sm

•Memory tab instructionStep Display... select Leaks and errors in the first combo box uncheck CRT Memory OK

•Memory tab instructionStep Refresh shows a much reduced set of data

All the data displayed is shown here - a much reduced set of information!

example-reducing-data-less

note Note the header helpfully shows the number of items hidden by the display settings, 62 compared with 2 before

example-reducing-data-header

The same approach could be done with other data, for example if you have allocations on other heaps:

•Memory tab instructionStep Display... uncheck Heap Memory uncheck Global Alloc Memory uncheck Local Alloc Memory OK Refresh

Or to remove handle allocations from the display:

•Memory tab instructionStep Display... uncheck Handles OK Refresh

note When you enable or disable the Memory Errors check box in the Memory tag display settings dialog, you may also need to make a change to the first combo box to make the display change. This is because memory error traces are not considered memory leaks.