Destroy streams created in rejected Promise.all() #609

matthew-white · 2022-09-16T04:00:06Z

Closes #482. See the commit message of the second commit for additional notes.

What has been done to verify that this works as intended?

I deployed this PR to the QA server and followed the reproduction steps in #482. As today and as expected, 9/10 concurrent requests were successful. However, unlike today, there was no database connection leak after the 10 responses.

We're not sure yet that we're going to ship this PR (see the next section). If we decide to, then I'll write unit tests of allWithStreams().

Why is this the best possible solution? Were any other approaches considered?

We want to add stream timeout functionality along the lines of #599/#604. However, we also want some way to destroy streams as soon as we know they can be. #604 (comment) mentions two options along those lines. This PR represents option 1, while #608 represents option 2.

I first tried running with option 2. However, when @alxndrsn ran the benchmarker against #608, the results were lackluster. I've pushed this PR in part so that @alxndrsn can run the benchmarker against it. If the PR is more performant than #608 (as I think we expect), then we'll probably want to ship it (as part of either v1.5.3 or v2022.3).

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

The hope is that this PR fixes connection leak issues. However, there's a risk of regression with each of the three streaming endpoints that the PR modifies. I think that if the results from the benchmarker are good, that should help us gain confidence in the PR.

Does this change require updates to the API documentation? If so, please update docs/api.md as part of this PR.

No changes needed.

Before submitting this PR, please make sure you have:

run make test-full and confirmed all checks still pass OR confirm CircleCI build passes
verified that any code from external sources are properly credited in comments

Closes #482. This commit prevents the following sequence: - A stream is created within a Promise.all(). - The stream is to be processed after the Promise.all() is fulfilled. - However, another promise in the Promise.all() is rejected. - As a result, the Promise.all() as a whole is rejected. - As a result, the stream is never processed and isn't destroyed.

matthew-white · 2022-09-16T04:01:57Z

lib/util/stream.js

+// that resolves to a stream, then the fate of the stream will be tied to the
+// fate of each promise within `values`. If any promise is rejected, then the
+// stream will be immediately destroyed.
+const allWithStreams = (values) => {


I don't love the name allWithStreams(), but I couldn't think of anything better. 🤔

matthew-white · 2022-09-16T04:05:30Z

lib/util/stream.js

+ };
+
+ for (const value of values) {
+ Promise.resolve(value)


We usually call resolve() from lib/util/promise.js rather than call Promise.resolve() directly. However, resolve() isn't otherwise used in this file, and importing it resulted in ESLint errors: there are several variables in this file that are also named resolve. It feels preferable to use Promise.resolve() here rather than rename those variables or alias resolve().

matthew-white · 2022-09-16T04:07:24Z

lib/util/stream.js

+ if (result instanceof PartialPipe) {
+ for (const stream of result.streams) handleStream(stream);
+ } else if (typeof result === 'object' && result != null &&
+ typeof result.pipe === 'function') {


We need to be able to handle both a regular stream and a PartialPipe. It looks like Submissions.streamForExport() returns a promise of a PartialPipe, while SubmissionAttachments.streamForExport() returns a promise of a stream.

matthew-white · 2022-09-19T19:57:58Z

In #604, I ran the benchmarker against this PR (among other commits). This was surprising to me, but the results were decidedly lackluster.

@alxndrsn actually noticed that Backend crashed when he ran the benchmarker against this PR locally. @alxndrsn wrote on Slack:

i'm guessing it's cleaning up slightly too enthusiastically. that, or something isn't getting told that the stream is shut down... so that might indicate a bug in slonik / my slonik patch

In 3/4 of the CircleCI builds that #604 (comment) links to, the following error message can be seen:

request to http://localhost:8383/v1/projects/1/forms/250_questions/submissions.csv.zip?splitSelectMultiples=true&groupPaths=true&deletedFields=true failed, reason: connect ECONNREFUSED 127.0.0.1:8383

I think that's a sign that Backend is crashing. In the one build without that error, the benchmarker results were quite good. Hopefully there's a way for us to prevent Backend from crashing! Among all the commits tested, only this PR resulted in that error message, so I do think there's something in this PR specifically that's going wrong.

alxndrsn · 2022-09-20T11:14:51Z

The errors may also be bugs in pg, and may not be specific to this branch:

Observed on this branch:

ConnectionError: timeout exceeded when trying to connect
    at Object.createConnection (/odk/backend/node_modules/slonik/dist/src/factories/createConnection.js:54:23)
    at runNextTicks (internal/process/task_queues.js:60:5)
    at listOnTimeout (internal/timers.js:526:9)
    at processTimers (internal/timers.js:500:7)ConnectionError: timeout exceeded when trying to connect
    at Object.createConnection (/odk/backend/node_modules/slonik/dist/src/factories/createConnection.js:54:23)
    at runNextTicks (internal/process/task_queues.js:60:5)
    at listOnTimeout (internal/timers.js:526:9)
    at processTimers (internal/timers.js:500:7)ConnectionError: timeout exceeded when trying to connect
    at Object.createConnection (/odk/backend/node_modules/slonik/dist/src/factories/createConnection.js:54:23)
    at runNextTicks (internal/process/task_queues.js:60:5)
    at listOnTimeout (internal/timers.js:526:9)
    at processTimers (internal/timers.js:500:7)ConnectionError: timeout exceeded when trying to connect
    at Object.createConnection (/odk/backend/node_modules/slonik/dist/src/factories/createConnection.js:54:23)
    at runNextTicks (internal/process/task_queues.js:60:5)
    at listOnTimeout (internal/timers.js:526:9)
    at processTimers (internal/timers.js:500:7)ConnectionError: timeout exceeded when trying to connect
    at Object.createConnection (/odk/backend/node_modules/slonik/dist/src/factories/createConnection.js:54:23)
    at runNextTicks (internal/process/task_queues.js:60:5)
    at listOnTimeout (internal/timers.js:526:9)
    at processTimers (internal/timers.js:500:7)/odk/backend/node_modules/pg/lib/client.js:367
    if (this.activeQuery.name) {
                         ^

TypeError: Cannot read property 'name' of null
    at Client._handleParseComplete (/odk/backend/node_modules/pg/lib/client.js:367:26)
    at Connection.emit (events.js:400:28)
    at Connection.emit (domain.js:470:12)
    at /odk/backend/node_modules/pg/lib/connection.js:115:12
    at Parser.parse (/odk/backend/node_modules/pg-protocol/dist/parser.js:40:17)
    at Socket.<anonymous> (/odk/backend/node_modules/pg-protocol/dist/index.js:10:42)
    at Socket.emit (events.js:400:28)
    at Socket.emit (domain.js:470:12)
    at addChunk (internal/streams/readable.js:290:12)
    at readableAddChunk (internal/streams/readable.js:265:9)
    at Socket.Readable.push (internal/streams/readable.js:204:10)
    at TCP.onStreamRead (internal/stream_base_commons.js:188:23)
make: *** [Makefile:16: run] Error 1

This may be: brianc/node-postgres#2705

I have also seen the following when testing with another branch, while machine was under heavy load:

/odk/backend/node_modules/pg/lib/client.js:360
    this.activeQuery.handleCommandComplete(msg, this.connection)
                     ^

TypeError: Cannot read property 'handleCommandComplete' of null
    at Client._handleCommandComplete (/odk/backend/node_modules/pg/lib/client.js:360:22)
    at Connection.emit (events.js:400:28)
    at Connection.emit (domain.js:470:12)
    at /odk/backend/node_modules/pg/lib/connection.js:115:12
    at Parser.parse (/odk/backend/node_modules/pg-protocol/dist/parser.js:40:17)
    at Socket.<anonymous> (/odk/backend/node_modules/pg-protocol/dist/index.js:10:42)
    at Socket.emit (events.js:400:28)
    at Socket.emit (domain.js:470:12)
    at addChunk (internal/streams/readable.js:290:12)
    at readableAddChunk (internal/streams/readable.js:265:9)
    at Socket.Readable.push (internal/streams/readable.js:204:10)
    at TCP.onStreamRead (internal/stream_base_commons.js:188:23)
make: *** [Makefile:16: run] Error 1

This may be: brianc/node-postgres#1872

And also:

/odk/backend/node_modules/pg/lib/client.js:367
    if (this.activeQuery.name) {
                         ^

TypeError: Cannot read property 'name' of null
    at Client._handleParseComplete (/odk/backend/node_modules/pg/lib/client.js:367:26)
    at Connection.emit (events.js:400:28)
    at Connection.emit (domain.js:470:12)
    at /odk/backend/node_modules/pg/lib/connection.js:115:12
    at Parser.parse (/odk/backend/node_modules/pg-protocol/dist/parser.js:40:17)
    at Socket.<anonymous> (/odk/backend/node_modules/pg-protocol/dist/index.js:10:42)
    at Socket.emit (events.js:400:28)
    at Socket.emit (domain.js:470:12)
    at addChunk (internal/streams/readable.js:290:12)
    at readableAddChunk (internal/streams/readable.js:265:9)
    at Socket.Readable.push (internal/streams/readable.js:204:10)
    at TCP.onStreamRead (internal/stream_base_commons.js:188:23)

It may be a race condition where the activeQuery in pg/lib/client.js has been cleared while the connection to postgres is still returning messages, either live or buffered...

matthew-white · 2022-09-23T05:32:33Z

I think the next step is to rebase this PR on the master branch. I think I'll wait to do that until we patch Slonik on the master branch by merging #599 or a similar PR. Once I rebase the PR, it may be useful to:

Check whether Backend is crashing. (I see that Add benchmarker running on Github Actions #612 checks for that. ✨)
Check pg_stat_activity for a database connection leak at the end of the benchmarker.

alxndrsn · 2022-09-23T08:10:47Z

Check pg_stat_activity for a database connection leak at the end of the benchmarker.

PR for a script to do this at: #622

matthew-white · 2022-10-04T20:09:03Z

I've marked this PR as a draft while we finish working on #564.

matthew-white · 2023-03-22T02:34:08Z

Closing now that we've decided to close #634.

wip

d273b6d

matthew-white requested a review from alxndrsn September 16, 2022 04:00

matthew-white force-pushed the all-with-streams branch from dc03f7b to 3ba66bb Compare September 16, 2022 04:08

matthew-white commented Sep 16, 2022

View reviewed changes

matthew-white linked an issue Sep 16, 2022 that may be closed by this pull request

10 concurrent requests for OData feed results in database connection leak #482

Closed

matthew-white mentioned this pull request Sep 16, 2022

Minimal slonik patch for closing stream queries (release) #604

Merged

Base automatically changed from release to master September 22, 2022 05:26

matthew-white removed a link to an issue Oct 1, 2022

10 concurrent requests for OData feed results in database connection leak #482

Closed

matthew-white mentioned this pull request Oct 4, 2022

Immediately destroy stream created in rejected Promise.all() #634

Closed

matthew-white linked an issue Oct 4, 2022 that may be closed by this pull request

Immediately destroy stream created in rejected Promise.all() #634

Closed

matthew-white marked this pull request as draft October 4, 2022 20:07

matthew-white closed this Mar 22, 2023

matthew-white deleted the all-with-streams branch March 22, 2023 02:35

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Destroy streams created in rejected Promise.all() #609

Destroy streams created in rejected Promise.all() #609

matthew-white commented Sep 16, 2022 •

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Destroy streams created in rejected Promise.all() #609

Destroy streams created in rejected Promise.all() #609

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matthew-white commented Sep 16, 2022 • edited Loading

What has been done to verify that this works as intended?

Why is this the best possible solution? Were any other approaches considered?

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

Does this change require updates to the API documentation? If so, please update docs/api.md as part of this PR.

Before submitting this PR, please make sure you have:

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