dscache: Reduce log level of memcache failures.

dscache: Reduce log level of memcache failures.

Warning-level failures quickly pollute the AppEngine log space. This
change converts some of the more common warnings to Debug-level logs so
the Warning space remains reserved for higher attention calls.

Also add a warning about lock eviction poisoning to THERE BE DRAGONS
section of the doc.

BUG=

Committed: https://github.com/luci/gae/commit/6d785923cdc1615899a7632269e5e636a2300786

[dnj, 2016-05-29 16:29:14]

Description was changed from

==========
dscache: Reduce log level of memcache failures.

Warning-level failures quickly pollute the AppEngine log space. This
change converts some of the more common warnings to Info-level logs so
the Warning space remains reserved for higher attention calls.

BUG=
==========

to

==========
dscache: Reduce log level of memcache failures.

Warning-level failures quickly pollute the AppEngine log space. This
change converts some of the more common warnings to Info-level logs so
the Warning space remains reserved for higher attention calls.

Also add a warning about lock eviction poisoning to THERE BE DRAGONS
section of the doc.

BUG=
==========

[dnj, 2016-05-29 16:29:32]

Description was changed from

==========
dscache: Reduce log level of memcache failures.

Warning-level failures quickly pollute the AppEngine log space. This
change converts some of the more common warnings to Info-level logs so
the Warning space remains reserved for higher attention calls.

Also add a warning about lock eviction poisoning to THERE BE DRAGONS
section of the doc.

BUG=
==========

to

==========
dscache: Reduce log level of memcache failures.

Warning-level failures quickly pollute the AppEngine log space. This
change converts some of the more common warnings to Debug-level logs so
the Warning space remains reserved for higher attention calls.

Also add a warning about lock eviction poisoning to THERE BE DRAGONS
section of the doc.

BUG=
==========

[dnj, 2016-05-29 16:29:40]

dnj@chromium.org changed reviewers:
+ iannucci@chromium.org

[dnj, 2016-05-29 16:29:41]

PTAL

[dnj, 2016-05-29 16:29:47]

Patchset #1 (id:1) has been deleted

[iannucci, 2016-05-29 19:49:12]

lgtm

https://chromiumcodereview.appspot.com/1987353002/diff/20001/filter/dscache/d...
File filter/dscache/doc.go (right):

https://chromiumcodereview.appspot.com/1987353002/diff/20001/filter/dscache/d...
filter/dscache/doc.go:185: // bounding the period of time when poisoned data may
reside in the cache.
but even with this, there's potential for a sampling error: sample Statistics,
and read a big expiration value, flush happens, memcache.Put happens (with big
expiration value).

[dnj, 2016-05-29 21:25:18]

https://chromiumcodereview.appspot.com/1987353002/diff/20001/filter/dscache/d...
File filter/dscache/doc.go (right):

https://chromiumcodereview.appspot.com/1987353002/diff/20001/filter/dscache/d...
filter/dscache/doc.go:185: // bounding the period of time when poisoned data may
reside in the cache.
On 2016/05/29 19:49:12, iannucci wrote:
> but even with this, there's potential for a sampling error: sample Statistics,
> and read a big expiration value, flush happens, memcache.Put happens (with big
> expiration value).

Hmm we could do a post-Put Statistics grab and try to invalidate, but yeah.

[dnj, 2016-05-29 21:25:23]

The CQ bit was checked by dnj@chromium.org

[commit-bot: I haz the power, 2016-05-29 21:25:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1987353002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1987353002/20001

[commit-bot: I haz the power, 2016-05-29 21:28:06]

Description was changed from

==========
dscache: Reduce log level of memcache failures.

Warning-level failures quickly pollute the AppEngine log space. This
change converts some of the more common warnings to Debug-level logs so
the Warning space remains reserved for higher attention calls.

Also add a warning about lock eviction poisoning to THERE BE DRAGONS
section of the doc.

BUG=
==========

to

==========
dscache: Reduce log level of memcache failures.

Warning-level failures quickly pollute the AppEngine log space. This
change converts some of the more common warnings to Debug-level logs so
the Warning space remains reserved for higher attention calls.

Also add a warning about lock eviction poisoning to THERE BE DRAGONS
section of the doc.

BUG=

Committed:
https://github.com/luci/gae/commit/6d785923cdc1615899a7632269e5e636a2300786
==========

[commit-bot: I haz the power, 2016-05-29 21:28:07]

Committed patchset #1 (id:20001) as
https://github.com/luci/gae/commit/6d785923cdc1615899a7632269e5e636a2300786