# Debug your database with Flame Graphs

Flame Graphs are used as a debugging tool to identify latency and the part of the execution path that takes most of the CPU time.
Use Flame Graphs when you:

* Need to understand which ScyllaDB code path/functions are using the most time. For instance, when you have latency issues.
* Need to compare time spent in particular ScyllaDB code paths/functions on different shards. For instance, when you have latency issues on one CPU but not on the other.

## Run a Flame Graph

**Procedure**

1. Install flamegraph and flamegraph-stackcollapse-perf

   From DNF
   ```shell
   dnf install flamegraph.noarch flamegraph-stackcollapse-perf.noarch
   ```

   If the above packages are not available in you distribution’s repositories, you can clone the FlameGraph git repository
   ```shell
   git clone https://github.com/brendangregg/FlameGraph
   cd FlameGraph
   ```
2. Run the following perf commands, using [Map CPU to ScyllaDB Shards](https://docs.scylladb.com/manual/master/kb/map-cpu.md)  and [Using the perf utility with ScyllaDB](https://docs.scylladb.com/manual/master/kb/use-perf.md) for reference.
   ```shell
   sudo perf record --call-graph dwarf -C <CPU on which you are onrecording>
   sudo perf script | stackcollapse-perf.pl | flamegraph.pl > some_name.svg
   ```
3. The result is an .svg file that is not just a picture but a dynamic diagram where you can search, zoom in, and zoom out. In order to enjoy a Flame Graph properly with all of its features you can open it in a browser such as Chrome or Firefox.

![image](kb/flamegraph.svg)

## Tips

* On the CPU you are recording, try to load ScyllaDB to consume 100% of the CPU runtime. Otherwise you’ll see a lot of OS functions related to the idle time handling
* Recording on all shards (e.g. using “perf record” -p parameter) may lead to confusing results recording the same symbol called from different threads (shards). This is not recommended.