[GitHub] wohali opened a new pull request #563: Disable unstable JS _show ETag test

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

wohali opened a new pull request #563: Disable unstable JS _show ETag test
URL: https://github.com/apache/couchdb/pull/563
 
 
   The full discussion is in #559, but here is a summary.
   
   Through instrumentation of ddoc_cache and ets_lru I suspect that this is
   caused by cache eviction happening after the second GET. While I didn't
   instrument exactly where the GET occurs it's clear that it's fairly
   late, certainly after the PUT 201 is returned, and likely after the
   subsequent GET actually reads from ddoc_cache.
   
   After applying a change to allow me to completely disable the ddoc_cache
   (-ddoc_cache max_objects 0 in vm.args) I ran the test on a loop
   overnight, and the test never failed (>1000 executions). Previously the
   test would fail every 20-30 executions.
   
   TL;DR: we can't guarantee immediate ddoc_cache eviction on a ddoc
   update, even for a single .couch file on a single node. (For obvious
   reasons we definitely can't guarantee this in a cluster configuration.)
   
   I will document this as a backwards compatibility change in 2.0 and
   forward with a separate checkin to couchdb-documentation.
   
   Thanks to @rnewson @janl and @davisp for helping track this one down!
   
   This checkin also includes an improvement to the output when a JS test
   fails a notEquals assertion.
   
   Closes #559 
 
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