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Valgrind

This document explains how to use Valgrind to perform certain debug tasks.

Be aware that Valgrind has certain limitations, e.g. that its virtual machine online runs on a single core and that it only works well under Linux!

Build

Create a debug build that uses the system memory allocator (i.e. neither heappy nor jemalloc):

$ cargo build --no-default-features

For longer runs you may wanna use a release build. Just note that some traces are less precise when working with them:

$ cargo build --no-default-features --release

Memory Leaks

There is a script that does most of the config setting. Just start the server with:

$ ./scripts/valgrind_leak ./target/debug/influxdb_iox run ...

You can kill the server w/ CTRL-C when you're ready. The Valgrind output will be written to valgrind-out.txt.

Suppression Rules

Valgrind allows you to suppress certain outputs. This can be used to ignore known "issues" like that lazycell leaks. For IOx we provide a file that is used by the scripts (under scripts/valgrind.supp). If you plan to write your own rules, here are some useful links:

You may also use the --gen-suppressions=all to auto-generate suppression rules:

$ ./scripts/valgrind_leak --gen-suppressions=all ./target/debug/influxdb_iox run ...

Note that Rust symbols like influxdb_iox::main are mangled in a way that Valgrind cannot parse them (e.g. to _ZN12influxdb_iox4main17h940b8bf02831a9d8E). The easiest way is to replace :: w/ * and prepend and append an additional wildcard *, so influxdb_iox::main gets *influxdb_iox*main*.

Massif

Massif allows you to track memory usage over time. This is helpful when memory is not really leaked in a traditional sense (aka that allocated memory is not freed when the program exists) but when memory is accumulated in some data structures. Run Massif via (assuming you have a release build):

valgrind \
    --tool=massif \
    --detailed-freq=1 \
    --max-snapshots=100 \
    --threshold=0.1 \
    --time-unit=ms \
    ./target/release/influxdb_iox \
    run ...

You might wanna play around with the options a bit.

The simplest way to use the massif output is to use massif-visualizer:

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