The MCP SDK's EventStore Lives in Memory. Here's What Happens When Your Server Restarts.

I Built a Python Package to Fix SSE Resumability in the MCP SDK Your MCP server crashed. Your client reconnected. Every event from that session? Gone. The Gap The Model Context Protocol Python SDK ships with a built-in EventStore that powers SSE stream resumability — when a client reconnects with a Last-Event-ID header, the server replays the events it missed. This works great in development. The catch: that store lives entirely in memory. Restart the process, roll a new deployment, or — in a multi-worker setup — have the reconnecting client land on a different pod, and the session is gone. The store was local to the process that died. Resumability silently returns nothing. This isn't a bug in the SDK. It's a scope decision — the in-memory store is a correct, useful default for single-process development. But the moment you deploy to production, you need something durable. That's the gap mcp-persist fills. What It Does mcp-persist adds three drop-in EventStore backends — SQLite , Redis , and PostgreSQL — that survive process restarts and work across multi-worker deployments. Pick the one that fits your infrastructure; the API is identical across all three. pip install "mcp-persist[sqlite]" # no external service needed pip install "mcp-persist[redis]" # for multi-worker deployments pip install "mcp-persist[postgres]" # for teams already running Postgres The Two-Line Setup Wiring resumability by hand is tedious — you need a store, a StreamableHTTPSessionManager , a Starlette lifespan to open and close both, and a Mount . The with_persistence() helper collapses all of that. Pass your FastMCP instance, get back a runnable ASGI app: import uvicorn from mcp.server.fastmcp import FastMCP from mcp_persist import with_persistence mcp = FastMCP ( name = " MyServer " ) app = with_persistence ( mcp , backend = " sqlite " , url = " events.db " , ttl = 3600 ) uvicorn . run ( app , host = " 127.0.0.1 " , port = 8000 ) # MCP endpoint at /mcp Switching to Redis is a one-word change: