[GitHub] nickva opened a new pull request #1177: Avoid unconditional retries in replicator's http client

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

nickva opened a new pull request #1177: Avoid unconditional retries in replicator's http client
URL: https://github.com/apache/couchdb/pull/1177
 
 
   In some cases the higher level code from `couch_replicator_api_wrap` needs to
   handle retries explicitly and cannot cope with retries happening in the lower
   level http client. In such cases it sets `retries = 0`.
   
   For example:
   
   https://github.com/apache/couchdb/blob/master/src/couch_replicator/src/couch_replicator_api_wrap.erl#L271-L275
   
   The http client then should avoid unconditional retries and instead consult
   `retries` value. If `retries = 0`, it shouldn't retry and instead bubble the
   exception up to the caller.
   
   This bug was discovered when attachments were replicated to a target cluster
   and the target cluster's resources were constrainted. Since attachment `PUT`
   requests were made from the context of an open_revs `GET` request, `PUT`
   request timed out, and they would retry. However, because the retry didn't
   bubble up to the `open_revs` code, the second `PUT` request would die with a
   `noproc` error, since the old parser had exited by then. See issue #745 for
   more.
   
   ## Testing recommendations
   
   See issue #745 comments on how to set up testing. The code was tested locally with a Vagrant VM running Debian 8, Erlang 17.5. Hardware resources were 1 CPU, throttled to about 30%, disk throughput also throttled to about 10Mb/s. `stress` running in the background as `stress --timeout 900m --cpu 1 --io 4`.
   
   

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