Use multi-transactional iterators#2540
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nickva merged 1 commit intoprototype/fdb-layerfrom Feb 14, 2020
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Looks pretty good but I had a few different questions.
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Previously changes feeds would fail if they streamed data for more than five
seconds. This was because of the FoundationDB's transaction time limit. After
the timeout fired, an 1007 (transaction_too_long) error was raised, and
transaction was retried. The emitted changes feed would often crash or simple
hang because the HTTP state would be garbled as response data was re-sent over
the same socket stream again.
To fix the issue introduce a new `{restart_tx, true}` option for
`fold_range/4`. This option sets up a new transaction to continue iterating
over the range from where the last one left off.
To avoid data being resent in the response stream, user callback functions must
first read all the data they plan on sending during that callback, send it out,
and then after that it must not do any more db reads so as not to trigger a
`transaction_too_old` error.
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This is a 3rd approach.
Simplified even more after talking with @davisp
This one is driven by an optioned passed in to fold_range. There is also just a single fold_range callback as opposed to two as before.
Previous approach: #2532