Improve back-pressure mechanism for RxResult #882
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bigmontz
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Feb 28, 2022
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| const session = driver.rxSession() | ||
| const xs = [] | ||
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| const result = session.run('UNWIND RANGE(0, 10) AS x RETURN x') | ||
| result | ||
| .records() | ||
| .pipe(map(record => record.get('x').toInt())) | ||
| .subscribe({ | ||
| next: async x => { | ||
| xs.push(x) | ||
| // manual pushing reoords to the stream | ||
| // it pauses the automatic pushing | ||
| await result.push() | ||
| }, | ||
| complete: async () => { | ||
| expect(xs).toEqual([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) | ||
| await session.close().toPromise() | ||
| done() | ||
| }, | ||
| error: done.fail.bind(done) | ||
| }) |
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Usage for result.push api
bigmontz
commented
Feb 28, 2022
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| const session = driver.rxSession() | ||
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| try { | ||
| const result = session.run('UNWIND RANGE(0, 10) AS x RETURN x') | ||
| const xs = await result | ||
| .records() | ||
| .pipe( | ||
| map(record => record.get('x').toInt()), | ||
| bufferCount(5), // buffer 5 records | ||
| mergeMap(async theXs => { | ||
| // pausing the records coming from the stream | ||
| result.pause() | ||
| // some costly operation | ||
| await callCostlyApi(theXs) | ||
| // resume the stream | ||
| await result.resume() | ||
| return theXs | ||
| }), | ||
| toArray() | ||
| ) | ||
| .toPromise() | ||
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| expect(xs).toEqual([[0, 1, 2, 3, 4], [5, 6, 7, 8, 9], [10]]) | ||
| } finally { | ||
| await session.close().toPromise() | ||
| } |
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Examples for pause and resume
bigmontz
changed the title
rxSession
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The lack of consumer oriented back-pressure mechanism in the RxJS apis was causing memory issues and other problems in the client code.
For solving this issue, the records observer returned by
RxResult.records()was changed for using the async iterator as foundation. New methods for enabling the client for fine controlling the stream were added to theRxResultapi. These methods are:pause(): Pause the record streaming. No new record will be pushed to the stream utilpushorresumeget called.resume(): Resumes the records streaming.push(): Push the next record. If the stream is not paused, this method will pause it for giving the push control to the client.