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https://github.com/visemet/gdb-mongodb-server

GDB pretty printers and commands for debugging the MongoDB Server
https://github.com/visemet/gdb-mongodb-server

gdb mongo mongodb

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GDB pretty printers and commands for debugging the MongoDB Server

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README 

        
==================

gdb-mongodb-server

==================



About

=====



The *gdbmongo* package contains GDB pretty printers and commands for

debugging the MongoDB Server. Its primary target audience is MongoDB

employees.



Motivation

----------



The *gdbmongo* package is mostly born out of joy from tinkering with

low-level constructs while writing GDB pretty printers. There are some

explicit areas for what it aims to achieve:



1. GDB pretty printers and commands which only work against live MongoDB

   processes are of limited value. This is because the hang analyzer is

   only granted enough time in Evergreen to save a core file for each of

   the lingering processes. Further analysis is deferred until later by

   making use of these saved core files. GDB pretty printers and

   commands which are implemented by walking in-memory data structures

   and not by executing C++ code **can run against core dumps** and are

   therefore more widely applicable.



2. New versions of the MongoDB Server are released regularly. Each new

   git branch fragments the tooling for testing the server. This can

   cause development on older branches to feel foreign and awkward

   because so many new enhancements were made in the meantime. Flipping

   the model so there’s **a single version which attempts to work with

   all supported MongoDB versions** can potentially enable more things

   to “just work.” Another way to think about it is that the new GDB

   pretty printers and commands may not be getting built for new MongoDB

   Server functionality and instead may be getting built for a

   newly-recognized debugging need.



Installation

============



The *gdbmongo* package must be loaded into the Python installation that

the GDB process is running. In particular, launching ``gdb`` from within

a Python virtual environment won’t give the GDB process access to the

Python packages defined within the virtual environment. This is because

``gdb`` is dynamically linked against *libpython* and therefore always

uses the site-packages of the base installation.



Adding the following snippet to a .gdbinit file will cause ``gdb`` at

launch time to attempt to install the *gdbmongo* package if it isn’t

already installed.



.. code-block:: python



    # In your ~/.gdbinit:

    python

    try:

        import gdbmongo

    except ImportError:

        import sys

        if sys.prefix.startswith("/opt/mongodbtoolchain/"):

            import subprocess

            subprocess.run([sys.prefix + "/bin/python3", "-m", "pip", "install", "gdbmongo"], check=True)

            import gdbmongo

        else:

            import warnings

            warnings.warn("Not attempting to install gdbmongo into non MongoDB toolchain Python")



    if "gdbmongo" in dir():

        gdbmongo.register_printers()

    end



If you don’t plan to use the GDB pretty printers defined in the

mongodb/mongo repository then you may want to consider enabling some of

the other printers defined by the *gdbmongo* package by default.



.. pull-quote::



    register_printers(\*, essentials=True, stdlib=False, abseil=False, boost=False, mongo_extras=False)

        Register the pretty printers defined by the gdbmongo package with GDB itself.



        The pretty printer collections other than gdbmongo-essentials are defaulted to off to avoid

        conflicting with the pretty printers defined in the mongodb/mongo repository.



Regardless of whether you choose to enable these other pretty printers

by default, each of the gdbmongo-\* pretty printer collections can still

be enabled later on within GDB. For example, the gdbmongo-mongo-extras

pretty printer collection can be enabled with the following command:



.. code-block::



    (gdb) enable pretty-printer global gdbmongo-mongo-extras



*Tip*: Use ``info pretty-printer``, ``enable pretty-printer``,

``disable pretty-printer``, and ``print /r`` to inspect and toggle the

state of any GDB pretty printers.



Usage

=====



The *gdbmongo* package is a nascent GDB extension and quite limited in

what it can do right now. But, if you’re looking to dump the contents of

the global ``LockManager`` in a core dump, then you can run the

following commands:



.. code-block:: python



    (gdb) python lock_mgr = gdbmongo.LockManagerPrinter.from_global()

    (gdb) python print(lock_mgr.val)