Re: [Django] #29183: "cache" template tag should not render empty strings on failure

[Django]

#29183: "cache" template tag should not render empty strings on failure
-+-
 Reporter:  Nicolas Le Manchet   |Owner:  nobody
 Type:  Uncategorized|   Status:  closed
Component:  Core (Cache system)  |  Version:  2.0
 Severity:  Normal   |   Resolution:  invalid
 Keywords:  cache, template, | Triage Stage:
  memcached, pylibmc |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Tim Graham):

 * status:  new => closed
 * resolution:   => invalid


Comment:

 Marking as invalid since the cache template tag doesn't have the reported
 behavior.

-- 
Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

-- 
You received this message because you are subscribed to the Google Groups 
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to django-updates+unsubscr...@googlegroups.com.
To post to this group, send email to django-updates@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/django-updates/067.46e2621f7e0780a520ceda92ecce0006%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.

Re: [Django] #29183: "cache" template tag should not render empty strings on failure

[Django]

#29183: "cache" template tag should not render empty strings on failure
-+-
 Reporter:  Nicolas Le Manchet   |Owner:  nobody
 Type:  Uncategorized|   Status:  new
Component:  Core (Cache system)  |  Version:  2.0
 Severity:  Normal   |   Resolution:
 Keywords:  cache, template, | Triage Stage:
  memcached, pylibmc |  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Tim Graham):

 * easy:  1 => 0


Comment:

 The behavior is different on the master branch. As of
 e62165b898785e890661953c3b2c9c36d98aee57, `{% include %}` no longer
 silences exceptions. Do you want to propose a different behavior (such as
 `{% cache %}` silencing the exception)? I'm not sure whether or not there
 would be consensus to do that, but you could write to the
 DevelopersMailingList to get feedback.

-- 
Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

-- 
You received this message because you are subscribed to the Google Groups 
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to django-updates+unsubscr...@googlegroups.com.
To post to this group, send email to django-updates@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/django-updates/067.5a534726ad3b1aef41f7e4dc534830d5%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.

[Django] #29183: "cache" template tag should not render empty strings on failure

[Django]

#29183: "cache" template tag should not render empty strings on failure
-+-
   Reporter:  NicolasLM  |  Owner:  nobody
   Type: | Status:  new
  Uncategorized  |
  Component:  Core   |Version:  2.0
  (Cache system) |   Keywords:  cache, template,
   Severity:  Normal |  memcached, pylibmc
   Triage Stage: |  Has patch:  0
  Unreviewed |
Needs documentation:  0  |Needs tests:  0
Patch needs improvement:  0  |  Easy pickings:  1
  UI/UX:  0  |
-+-
 The cache template tag renders an empty string when a connection errors
 happens while fetching from the cache.

 I believe that the "cache" template tag should try to fetch from the
 cache, but fall back to being a noop in case of error.

 **Example:**

 An included template contains an expensive calculation wrapped in a cache
 tag:
 {{{
 
 {% cache 600 cleaned_article article.id %}{{ article.content |
 clean_article | safe }}{% endcache %}
 
 }}}

 If any error happens while fetching from the cache, the included template
 is rendered as an empty string and the following warning is printed in
 logs:
 {{{
 [2018-03-03 17:36:08,140 WARNI waitress django.template] Exception raised
 while rendering {% include %} for template 'reader/home.html'. Empty
 string rendered instead.
 Traceback (most recent call last):
   File "/usr/local/lib/python3.6/site-
 packages/django/template/loader_tags.py", line 194, in render
 return template.render(context)
   File "/usr/local/lib/python3.6/site-packages/django/template/base.py",
 line 177, in render
 return self._render(context)
   File "/usr/local/lib/python3.6/site-packages/django/test/utils.py", line
 98, in instrumented_test_render
 return self.nodelist.render(context)
   File "/usr/local/lib/python3.6/site-packages/django/template/base.py",
 line 943, in render
 bit = node.render_annotated(context)
   File "/usr/local/lib/python3.6/site-packages/django/template/base.py",
 line 910, in render_annotated
 return self.render(context)
   File "/usr/local/lib/python3.6/site-
 packages/django/template/defaulttags.py", line 211, in render
 nodelist.append(node.render_annotated(context))
   File "/usr/local/lib/python3.6/site-packages/django/template/base.py",
 line 910, in render_annotated
 return self.render(context)
   File "/usr/local/lib/python3.6/site-
 packages/django/templatetags/cache.py", line 45, in render
 value = fragment_cache.get(cache_key)
   File "/usr/local/lib/python3.6/site-
 packages/django/core/cache/backends/memcached.py", line 73, in get
 val = self._cache.get(key)
 pylibmc.ConnectionError: error 3 from
 memcached_get(:1:template.cache.cleaned_articl): (0x7faf5c0cee70)
 CONNECTION FAILURE, ::rec() returned zero, server has disconnected,  host:
 memcached:11211 -> libmemcached/io.cc:484
 }}}

 Cache settings:
 {{{
 CACHES = {
 'default': {
 'BACKEND': 'django.core.cache.backends.memcached.PyLibMCCache',
 'TIMEOUT': 24 * 60 * 60,
 'LOCATION': 'memcached:11211',
 'OPTIONS': {
 'binary': True,
 'behaviors': {
 'no_block': True,
 'tcp_nodelay': True,
 'tcp_keepalive': True,
 'connect_timeout': 2000,  # ms
 'send_timeout': 750 * 1000,  # us
 'receive_timeout': 750 * 1000,  # us
 '_poll_timeout': 2000,  # ms
 'ketama': True,
 'remove_failed': 1,
 'retry_timeout': 2,
 'dead_timeout': 30,
 }
 }
 }
 }
 }}}

 **Additional information:**
 Django 2.0.2
 Python 3.6.4
 Linux 4.9.82

 Both the Django application and Memcached run on Docker containers on the
 same host. The error happens after a restart of Memcached (but no restart
 of the Django container) because pylibmc reuses connections between
 requests and it cannot detect that connections should be discarded because
 of the Docker userland proxy.

-- 
Ticket URL: 
Django 
The Web framework for perfectionists with deadlines.

-- 
You received this message because you are subscribed to the Google Groups 
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email 
to django-updates+unsubscr...@googlegroups.com.
To post to this group, send email to django-updates@googlegroups.com.
To view this discussion on the web visit 
https://groups.google.com/d/msgid/django-updates/052.b83d3572b444bee805e6ff9294e2b0b9%40djangoproject.com.
For more options, visit