chore: better debugging with gdb (#145)

* Add nix wrapper for GDB. This is added to docs.

* Use `log_min_messages=INFO` by default for better debugging.

* Add tags to gitignore.

Author: steve-chavez

.gitignore

@@ -13,3 +13,4 @@ nix/nginx/logs/nginx.pid
 *.control
 *.so
 nginx.pid
+tags

docs/contributing.md

@@ -56,6 +56,24 @@ select net.http_get('http://localhost:3000/projects');
 -- * Connection #0 to host localhost left intact
 ```
 
+### GDB
+
+To debug the background worker, grab its PID from the logs:
+
+```
+$ nix-shell
+$ net-with-pg-16 psql
+
+2024-09-02 20:16:26.905 -05 [1145879] INFO:  pg_net_worker started with a config of: pg_net.ttl=6 hours, pg_net.batch_size=200, pg_net.database_name=postgres
+```
+
+And use it like:
+
+```
+$ nix-shell
+$ sudo with-gdb -p 1145879
+```
+
 ## Documentation
 
 All public API must be documented. Building documentation requires python 3.6+

nix/gdbScript.nix

@@ -0,0 +1,12 @@
+{ gdb, writeText, writeShellScriptBin } :
+
+let
+  file = writeText "gdbconf" ''
+    # Do this so we can do `backtrace` once a segfault occurs. Otherwise once SIGSEGV is received the bgworker will quit and we can't backtrace.
+    handle SIGSEGV stop nopass
+  '';
+  script = ''
+    ${gdb}/bin/gdb -x ${file} "$@"
+  '';
+in
+writeShellScriptBin "with-gdb" script

nix/pgScript.nix

@@ -2,7 +2,7 @@
 
 let
   LOGMIN = builtins.getEnv "LOGMIN";
-  logMin = if builtins.stringLength LOGMIN == 0 then "WARNING" else LOGMIN; # warning is the default in pg
+  logMin = if builtins.stringLength LOGMIN == 0 then "INFO" else LOGMIN;
   ver = builtins.head (builtins.splitVersion postgresql.version);
   script = ''
     set -euo pipefail

nix/pg_net.nix

@@ -7,6 +7,9 @@ stdenv.mkDerivation {
 
   src = ../.;
 
+  # this is enough for enabling debug info
+  dontStrip = true;
+
   installPhase = ''
     mkdir -p $out/bin
     install -D pg_net.so -t $out/lib

shell.nix

@@ -24,6 +24,7 @@ mkShell {
       extAll = map (x: callPackage ./nix/pgScript.nix { postgresql = pgWithExt { pg = x;}; }) supportedPgVersions;
       nginxScript = callPackage ./nix/nginxScript.nix {};
       pathodScript = callPackage ./nix/pathodScript.nix { mitmproxy = oldNixpkgs.mitmproxy; };
+      gdbScript = callPackage ./nix/gdbScript.nix {};
       pythonDeps = with python3Packages; [
         pytest
         psycopg2
@@ -37,6 +38,7 @@ mkShell {
       format.do format.doCheck
       nginxScript
       pathodScript
+      gdbScript
     ];
   shellHook = ''
     export HISTFILE=.history