varnish 2.0.4 questions - no IMS, no persistence cache - please help

Tollef Fog Heen tfheen at
Fri Oct 23 08:00:57 CEST 2009

]] GaneshKumar Natarajan 

| 1. varnish doesn't send IMS request, when the object expires.

Correct.  This is somewhat hard to do, but we see the request coming in
regularly so it's something we might want to change at some point.  I
don't believe there is any way to achieve this using VCL.

| 2. Varnish cache is not persistent.

Correct, this is being fixed for 2.1.  (It's the major feature for 2.1.)

| 3. mmap storage : max i can configure is 340 GB.
| detail::
| I was able to use only 340 GB of cache. any size after this, i would get error.
| child (25790) Started
| Pushing vcls failed: dlopen(./ ./
| failed to map segment from shared object: Cannot allocate memory

This looks weird.  Can you tell us something about what OS and kernel
versions you are running?

| 4. I tried malloc storage option.
| Question:
| i have system of 32 GB physical ram and my swap storage is 65 GB.
| harddisk storage - 1.5 TB ( distribued in 5 cache directoreys
| /cach0,.../cache1 ).
| What is the best optimal malloc storage i can use to achive greater performance?
| -s malloc, [ size ] ???

It depends on your setup and your traffic patterns, so it's usually best
to try some different ones.

| 5. what is the difference between using malloc or mmap?
| Help me to move onto varnish world and convince others in my team.

malloc is, well, using malloc to allocate the memory, letting the system
swap handle any page-outs.  mmap is just mmap-ing a large file, which
still leaves it to the system to page out the unused bits, but often
somewhat different code paths.  Which one is better depends on OS,
traffic pattern, amount of memory, etc.

Tollef Fog Heen 
Redpill Linpro -- Changing the game!
t: +47 21 54 41 73

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