add configuration for coredumps and document how to make sure they ar…

…e enabled

.devcontainer/.vscode/launch.json

@@ -16,5 +16,25 @@
                 }
             ],
         },
-    ]
-}
+        {
+            "name": "Open core file",
+            "type": "cppdbg",
+            "request": "launch",
+            "program": "/home/citus/.pgenv/pgsql/bin/postgres",
+            "coreDumpPath": "${input:corefile}",
+            "cwd": "${workspaceFolder}",
+            "MIMode": "gdb",
+        }
+    ],
+    "inputs": [
+        {
+            "id": "corefile",
+            "type": "command",
+            "command": "extension.commandvariable.file.pickFile",
+            "args": {
+                "dialogTitle": "Select core file",
+                "include": "**/core*",
+            },
+        },
+    ],
+}

.devcontainer/Dockerfile

@@ -152,6 +152,7 @@ RUN sudo apt update \
     lsof \
     man \
     net-tools \
+    psmisc \
     pspg \
     tree \
     vim \

.devcontainer/devcontainer.json

@@ -2,8 +2,11 @@
     "image": "ghcr.io/citusdata/citus-devcontainer:main",
     "runArgs": [
         "--cap-add=SYS_PTRACE",
+        "--ulimit=core=-1",
+    ],
+    "forwardPorts": [
+        9700
     ],
-    "forwardPorts": [9700],
     "customizations": {
         "vscode": {
             "extensions": [
@@ -14,6 +17,7 @@
                 "github.vscode-pull-request-github",
                 "ms-vscode.cpptools-extension-pack",
                 "ms-vsliveshare.vsliveshare",
+                "rioj7.command-variable",
             ],
             "settings": {
                 "files.exclude": {
@@ -29,4 +33,4 @@
     ],
     "updateContentCommand": "./configure",
     "postCreateCommand": "make -C .devcontainer/",
-}
+}

DEVCONTAINER.md

@@ -0,0 +1,43 @@
+# Devcontainer
+
+## Coredumps
+When postgres/citus crashes, there is the option to create a coredump. This is useful for debugging the issue. Coredumps are enabled in the devcontainer by default. However, not all environments are configured correctly out of the box. The most important configuration that is not standardized is the `core_pattern`. The configuration can be verified from the container, however, you cannot change this setting from inside the container as the filesystem containing this setting is in read only mode while inside the container.
+
+To verify if corefiles are written run the following command in a terminal. This shows the filename pattern with which the corefile will be written.
+```bash
+cat /proc/sys/kernel/core_pattern
+```
+
+This should be configured with a relative path or simply a simple filename. When your environment shows an absolute path you will need to change this setting. How to change this setting depends highly on the underlying system as the setting needs to be changed on the kernel of the host running the container.
+
+When a coredump is written you can use the debug/launch configuration `Open core file` which is preconfigured in the devcontainer. This will open a fileprompt that lists all coredumps that are found in your workspace. When you want to debug coredumps from `citus_dev` that are run in your `/data` directory, you can add the data directory to your workspace. In the command pallet of vscode you can run `>Workspace: Add Folder to Workspace...` and select the `/data` directory. This will allow you to open the coredumps from the `/data` directory in the `Open core file` debug configuration.
+
+### Windows (docker desktop)
+When running in docker desktop on windows you will most likely need to change this setting. The linux guest in WSL2 that runs your container is the `docker-desktop` environment. The easiest way to get onto the host, where you can change this setting, is to open a powershell window and verify you have the docker-desktop environment listed.
+
+```powershell
+wsl --list
+```
+
+Among others this should list both `docker-desktop` and `docker-desktop-data`. You can then open a shell in the `docker-desktop` environment.
+
+```powershell
+wsl -d docker-desktop
+```
+
+Inside this shell you can verify that you have the right environment by running
+
+```bash
+cat /proc/sys/kernel/core_pattern
+```
+
+This should show the same configuration as the one you see inside the devcontainer. You can then change the setting by running the following command.
+
+TODO: verify this:
+This will change the setting for the current session. If you want to make the change permanent you will need to add this to a startup script.
+
+```bash
+echo "core" > /proc/sys/kernel/core_pattern
+```
+
+You can put any other pattern in there as you see fit. This pattern is conservative and will overwrite the core on every crash.