Fix: Improve Custom MCP node performance by caching toolkits

[toi500]

As discussed, this PR fixes a critical performance issue in the Custom MCP node caused by redundant process spawning. The STDIO transport is re-spawning a child process on every UI refresh, leading to significant overhead.

Solution:

This is a single file solution implemented entirely within customMCP.ts.

1. A static toolkitCache is used to store and reuse MCPToolkit instances, preventing the expensive process creation on every refresh.
2. The cache key is generated by parsing the mcpServerConfig JSON. This makes the cache immune to formatting differences (spaces, newlines) and prevents spawning duplicate processes for the same logical configuration.

Trade-off:

Since we are not modifying core.ts and the node's destroy() method has proven unreliable for cleanup (I have tried to implement it without any success), this solution will leak one process per unique server configuration. This is a necessary trade-off to fix the critical performance issue immediately while keeping the changes isolated to this single file.

[toi500]

@HenryHengZJ, this is working very well for me now, very smooth.

I really hope you can find a solution to flush the cache when the custom node is deleted. I tried to implement this myself but without any success.

I will definitely be keeping this change for my own use, as it is much better to have a minor memory leak (especially since the current MCP implementation has some leaks anyway) than to have the constant process churn overload my server and force me to spend 20 minutes filling in actions on a single MCP node.

[Copilot]

Pull Request Overview

Implements caching for MCPToolkit instances to eliminate redundant process spawning on UI refresh, boosting performance.

• Introduces a static toolkitCache keyed by workspace, parsed config, and sandbox.
• Parses and canonicalizes mcpServerConfig to generate consistent cache keys.
• Clears out invalid mcpActions after loading a new toolkit to keep the UI in sync.

Comments suppressed due to low confidence (1)

packages/components/nodes/tools/MCP/CustomMCP/CustomMCP.ts:161

• Add unit tests to verify that cached toolkits are returned correctly and that the stale-action clearing logic behaves as expected to prevent regressions.

        if (Custom_MCP.toolkitCache.has(cacheKey)) {

[Copilot]

Serializing the entire sandbox object for the cache key can be expensive and may fail on circular references. Consider restricting the key to only the relevant sandbox properties (e.g. $vars), or use a lightweight hash of workspaceId and canonicalConfig instead.

Suggested change

	const cacheKey = JSON.stringify({ workspaceId, canonicalConfig, sandbox })
	const sandboxVars = sandbox['$vars'] || {};
	const cacheKey = JSON.stringify({ workspaceId, canonicalConfig, sandboxVars });

[HenryHengZJ]

@toi500 im quite concerned about stringify the whole canonicalConfig and sandboxVars because users can enter anything that could cause problem.

all we need is a unique key right?
how bout workspaceId_chatflowId_nodeId ?

[HenryHengZJ]

Nevermind, I think the key must be unique depending on the mcpServerConfig..

How do we clear the cache though?

[ahmedrowaihi]

does this takes care of tool availability changes ? when custom mcps are used via npx the mcp tools might change ( which is desired if user wants new version of that mcp server ), but I wonder this cache will not affect that ?

[toi500]

does this takes care of tool availability changes ? when custom mcps are used via npx the mcp tools might change ( which is desired if user wants new version of that mcp server ), but I wonder this cache will not affect that ?

Not sure if I am following you here. Every time you add a version, it uses a new mcpServerConfig, and you will fetch whatever actions that version has. That version is then cached until Flowise restarts.

If what you mean is that you will lose the convenience of using "@latest" in some cases, it is a trade-off I would definitely pay for not spinning up the same server 10 times to add 10 actions and spending 10 minutes on it.

[toi500]