[GitHub] [couchdb] nickva opened a new pull request #2670: Handle transaction cancelled errors in list_dbs_info/3

[GitBox <gi...@apache.org>]

nickva opened a new pull request #2670: Handle transaction cancelled errors in list_dbs_info/3
URL: https://github.com/apache/couchdb/pull/2670
 
 
   ### Overview 
   
   `list_dbs_info/3` maintains a queue of up to 100 futures which are used to
   concurrently fetch data. Previously, if the transaction was reset, and the
   accumulator inside the fold may have had futures from a previous transaction,
   which have gotten their results yet, they threw a transaction_canceled (1025)
   error.
   
   To fix this, if we're in a read-only transaction, we return the tx object in
   the opaque db info record. Then, if `erlfdb:wait/1` throws a transaction
   canceled error, we re-fetch the future from the now restarted transaction.
   
   Potentially, the transaction may also time-out while the futures queues is
   drained after the main range fold has finished already. Handle that case by
   reseting the transaction and then re-fetching the futures. To avoid an infinite
   loop we allow up to 2 retries only.
   
   This approach is not the most optimal but simpler as it hides the complexity
   inside the fabric2_fdb module where we already handle these conditions. It
   means that every 5 or so seconds we might have to refetch less than 100 extra
   futures from the queue (as some or all may have gotten their results back
   already).
   
   ### Testing recommendations
   
   ```
   make check-fdb
   ```
   
   Then check coverage in fabric2_fdb with `open src/fabric/.eunit/index.html`

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[GitHub] [couchdb] nickva merged pull request #2670: Handle transaction cancelled errors in list_dbs_info/3

[GitBox <gi...@apache.org>]

nickva merged pull request #2670: Handle transaction cancelled errors in list_dbs_info/3
URL: https://github.com/apache/couchdb/pull/2670
 
 
   

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