Debugging with mdb

Even when running on Linux, it is possible to debug node memory issues using mdb, the illumos debugger: MDB and Linux.

1. Generate a core dump of the node process using gcore.

2. Install the Manta utilities. Even if they conflict with existing binaries, the commands can be run directly from /usr/lib/node_modules/manta/bin/.

3. Copy the node binary and the core file into a debug directory.

4. Per the installation instructions, export Manta environment vars.

   Upload node and core using mput:

   tar cz debug | mput ~~/stor/debug.tar.gz

5. Follow the instructions to create and run mmdb.sh:

   ./mmdb.sh ~~/stor/debug.tar.gz

In mdb, use ::findjsobjects and ::jsprint to navigate and print objects:

• Use ::findjsobjects to find one representative of every kind of object

• Use abcd1234::findjsobjects | ::findjsobjects to find all objects like abcd1234

• Use abcd1234::findjsobjects -r to find all objects with a reference to abcd1234

Inspect stack frames and functions using ::jsframe, ::v8print and other commands:

• ::jsprint doesn’t say much about function objects; use ::v8print first on the function and then on the associated SharedFunctionInfo