[GitHub] wohali opened a new pull request #501: Fix error on race condition in mem3 startup

[gi...@git.apache.org]

wohali opened a new pull request #501: Fix error on race condition in mem3 startup
URL: https://github.com/apache/couchdb/pull/501
 
 
   During mem3 startup, 2 paths attempt to call `couch_server:create/2` on
   `_dbs`:
   
   ```
   gen_server:init_it/6
     -> mem3_shards:init/1
       -> mem3_shards:get_update_seq/0
         -> couch_server:create/2
   ```
   
   and
   
   ```
   mem3_sync:initial_sync/1
     -> mem3_shards:fold/2
       -> couch_server:create/2
   ```
   
   Normally, the first path completes before the second. If the second path
   finishes first, the first path fails because it does not expect a
   `file_exists` response.
   
   This patch simply retries mem3_util:ensure_exists/1 once if it gets back
   a `file_exists` response. Any failures past this point are not handled.
   
   Fixes COUCHDB-3402.
   
   /cc @davisp @nickva 
 
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