Why varnish ban requests not removing/invalidating cached data? - varnish

Question

I am trying to debug inconsistent behavior with varnish.
I have an application in which when a piece of content is updated a ban request is issued to varnish in order to remove it from cache and invalidate that cache. The problem is that this works fine just a few times but not in the majority of times although I can see the bans in the varnish log. Just to rephrase, when I save a piece of content, a ban is issued to varnish of the form
1374003254.031996 75 req.http.host ~ www.example.com && req.url ~ ^(.*)(?<!\d{1})539250(?!\d{1}) where 539250 is the unique content id present in the url.
I logged into the varnish host and check the varnish process. Executing ps -ef |grep varn gives
root 8889 1 0 15:19 ? 00:00:00 /usr/sbin/varnishd -P /var/run/varnish.pid -a :80 -T :8100 -f /etc/varnish/qa.vcl -u varnish -g varnish -h critbit -p http_max_hdr 256 -p thread_pool_min 200 -p thread_pool_max 4000 -p thread_pools 2 -p thread_pool_stack 262144 -p thread_pool_add_delay 2 -p session_linger 100 -p sess_timeout 60 -p listen_depth 4096 -p lru_interval 20 -p ban_lurker_sleep 0.2 -s malloc,1G
varnish 8897 8889 0 15:19 ? 00:00:00 /usr/sbin/varnishd -P /var/run/varnish.pid -a :80 -T :8100 -f /etc/varnish/qa.vcl -u varnish -g varnish -h critbit -p http_max_hdr 256 -p thread_pool_min 200 -p thread_pool_max 4000 -p thread_pools 2 -p thread_pool_stack 262144 -p thread_pool_add_delay 2 -p session_linger 100 -p sess_timeout 60 -p listen_depth 4096 -p lru_interval 20 -p ban_lurker_sleep 0.2 -s malloc,1G
Is it Normal to have 2 processes?
then I did an ban.list in the varnish cli:
1374003254.031996 75 req.http.host ~ example.com && req.url ~ ^(.*)(?<!\d{1})539250(?!\d{1})
1374003202.365076 224G req.http.host ~ example.com && req.url ~ ^(.*)(?<!\d{1})539250(?!\d{1})
1374003116.772315 83G req.http.host ~ example.com && req.url ~ ^(.*)(?<!\d{1})539250(?!\d{1})
1374002967.450431 267G req.http.host ~ example.com && req.url ~ ^(.*)(?<!\d{1})539250(?!\d{1})
1374002756.701640 187G req.http.host ~ example.com && req.url ~ ^(.*)(?<!\d{1})539250(?!\d{1})
All I want to know if there is somthing wrong causing the ban not remove cached data.

Answer 1

Your varnish process lines are looking good.
Varnish has a management process which starts (and watches over) a child where all the request handling is done. These are the two processes you are seeing.
If you do a lot of bans, you should consider reading the "Smart bans" chapter in the Varnish book. It will help you keep the list of bans shorter.
https://www.varnish-software.com/static/book/Cache_invalidation.html#smart-bans