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Merged
merged 5 commits into from
Aug 29, 2025
Merged

mcp/streamable: use event store to fix unbounded memory issues #335

merged 5 commits into from
Aug 29, 2025

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@samthanawalla
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@samthanawalla samthanawalla commented Aug 20, 2025

This CL utilizes the event store to write outgoing messages and removes the unbounded outgoing data structure.

For #190

@samthanawalla samthanawalla marked this pull request as ready for review August 20, 2025 15:47
@samthanawalla samthanawalla requested review from findleyr and jba August 20, 2025 15:47
jba
jba requested changes Aug 20, 2025
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findleyr reviewed Aug 22, 2025
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jba
jba requested changes Aug 25, 2025
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Sorry that this PR is confusing me so much.
I think I need to see the algorithm as a whole, without diffs.
So if you think it is correct after addressing my comments that it is correct, I'll approve and then read it separately.

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samthanawalla commented Aug 25, 2025

Sorry that this PR is confusing me so much. I think I need to see the algorithm as a whole, without diffs. So if you think it is correct after addressing my comments that it is correct, I'll approve and then read it separately.

Sorry I prematurely sent a new commit- not ready for review yet! (The flow is very confusing, I agree)

@samthanawalla samthanawalla marked this pull request as draft August 25, 2025 19:23
@samthanawalla
mcp/streamable: use event store to fix unbounded memory issues
cc0566e 
This CL utilizes the event store to write outgoing messages and removes
the unbounded outgoing data structure.

For modelcontextprotocol#190
@samthanawalla
remove lastWriteIndex and register stream with event store when created
bf2306e
samthanawalla
samthanawalla commented Aug 27, 2025
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@samthanawalla samthanawalla marked this pull request as ready for review August 27, 2025 14:19
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samthanawalla commented Aug 27, 2025 •
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Ready for review. The challenge is now with properly yielding the eventstore.After error.
Yielding this error immediately is not quite right since the eventstore.Append could happen after messages is called.

So we can either:

  1. skip streamid/session does not exist errors but yield other errors (PurgedError)
  2. skip yielding all eventstore errors and wait for an Append
  3. add some other synchronization methods such as eventstore.Start()

We can discuss IRL if that's better.

@samthanawalla samthanawalla requested review from findleyr and jba August 27, 2025 14:30
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findleyr commented Aug 27, 2025

@jba and I were discussing yesterday, and he also suggested adding something like EventStore.Start. What should it be called though?

We could use this to allow customizing the stream id...
Here are a few options

  • the name could be NewStream, StartStream, OpenStream
  • The signature could be func(StreamID) (accept a stream id) or func() StreamID (return a stream id).

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samthanawalla commented Aug 27, 2025

@jba and I were discussing yesterday, and he also suggested adding something like EventStore.Start. What should it be called though?

We could use this to allow customizing the stream id... Here are a few options

  • the name could be NewStream, StartStream, OpenStream
  • The signature could be func(StreamID) (accept a stream id) or func() StreamID (return a stream id).

Sounds good. Latest commit adds the EventStore.Open

jba
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mcp/event.go
// Open prepares the event store for a given session. It ensures that the
// underlying data structure for the sessionID is initialized, making it
// ready to store event streams.
Open(_ context.Context, sessionID string, streamID StreamID) error
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Does this need to be called once per session, or once per stream? If the latter, the doc is wrong.

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Looks like once per stream.

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@samthanawalla samthanawalla Aug 28, 2025

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Done

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Maybe we should call this OpenStream or StartStream to make that clearer? I'd be fine with either.

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Everything is XXXStream. Append to stream, get messages from stream. The only session method has "Session" in the name. So "Open" is right.

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I said that badly. I meant that EventStore.M is about streams unless M explicitly says otherwise.

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Also, Open takes a stream ID, so of course it is opening a stream.

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findleyr reviewed Aug 29, 2025
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LGTM, just want to revisit the name 'Open'.

mcp/event.go
// Open prepares the event store for a given session. It ensures that the
// underlying data structure for the sessionID is initialized, making it
// ready to store event streams.
Open(_ context.Context, sessionID string, streamID StreamID) error
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Maybe we should call this OpenStream or StartStream to make that clearer? I'd be fine with either.

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jba commented Aug 29, 2025

The challenge is now with properly yielding the eventstore.After error. Yielding this error immediately is not quite right since the eventstore.Append could happen after messages is called.

So we can either:

  1. skip streamid/session does not exist errors but yield other errors (PurgedError)
  2. skip yielding all eventstore errors and wait for an Append
  3. add some other synchronization methods such as eventstore.Start()

We can discuss IRL if that's better.

Not sure I understand. An error from After should mean that things are broken: the session or stream is unknown, the data you need is gone, the underlying storage has failed, etc. It's not an error to exhaust the available messages (even there are zero). The outer loop in messages takes care of Appends that come later. I think Open fixes the "unknown" case, right?

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samthanawalla commented Aug 29, 2025

The challenge is now with properly yielding the eventstore.After error. Yielding this error immediately is not quite right since the eventstore.Append could happen after messages is called.
So we can either:

  1. skip streamid/session does not exist errors but yield other errors (PurgedError)
  2. skip yielding all eventstore errors and wait for an Append
  3. add some other synchronization methods such as eventstore.Start()

We can discuss IRL if that's better.

Not sure I understand. An error from After should mean that things are broken: the session or stream is unknown, the data you need is gone, the underlying storage has failed, etc. It's not an error to exhaust the available messages (even there are zero). The outer loop in messages takes care of Appends that come later. I think Open fixes the "unknown" case, right?

Yes Open fixes the unknown case now.

@samthanawalla samthanawalla enabled auto-merge (squash) August 29, 2025 15:33
@samthanawalla samthanawalla merged commit ddaf35e into modelcontextprotocol:main Aug 29, 2025
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@samthanawalla samthanawalla deleted the fixMemoryIssue branch September 11, 2025 18:17
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@samthanawalla @findleyr @jba