This repository contains the dynamic tracing scripts and documentation about BPF and BCC. It is mainly geared towards MemSQL performance engineers who may want to write BPF scripts, but it may be useful to the general public as some basic examples of BPF and BCC.

docs/ contains various text files including notes and presentations.

tools/ contains the BPF/BCC programs

patches/ includes some patches for BCC to get some of my tools working

Before reading anything but the Introduction, I would recommend reading the BCC project's README and [their documentation] (https://github.com/iovisor/bcc/tree/master/docs).

Introduction - An introduction to (mostly Linux) tracing technologies.

BPF - what is BPF and how to write it

Kernel - information about kernel internals sometimes useful for writing certain kinds of scripts

BCC - tips and tricks regarding the BPF Compiler Collection (BPF)

These scripts vary in their level of completion. Note also that these tools are meant primarily as a resource for people looking to use BCC / BPF. Support for USDT probes in MemSQL is experimental and versions of MemSQL earlier than 5.1.3 do not support any USDT probes.

Scripts that work:

• query_latency.py - simple script that traces queries' latencies. Can filter on plan ID.
• query_memory.py - traces queries' memory usage. Can filter on plan ID.
• futexes.py - traces futex syscalls' latencies. Can filter on process and query plan ID. Note that when filtering it tends to hang after a few seconds. Not sure why.
• partition.py - Traces the probes for all the low-level commands in the clustering / partition sharding code. Make sure you point it at the exact binary from which the node you want to trace was launched. See the help for this tool, or [the MemSQL BPF doc's debugging section] (docs/02_bpf.md#your-probe-which-counts-something-like-probe-hits-attaches-without-errors-but-it-is-reporting-a-count-of-0) for more info.

Scripts that don't work:

• query_bio.py - Derived from the bcc biosnoop utility, but augmented to support filtering based on query.
• query_tsa.py - A script for thread-state analysis. For some reason, some of the important probe instrumentation appears not to be firing. Uses kernel tracepoints, and thus requires Linux version >= 4.7
• query_tsa_old.py - Like query_tsa.py, but does not use tracepoints, and is in less of a working state.

To those not using MemSQL, query_tsa.py and futexes.py probably will be most interesting.