On 08/24/2015 04:47 PM, Jan Kaluža wrote:
Hi,
unfortunately, the r1680920 brought undesired behavior described in PR
58267 to 2.2.x. The bug is well described in the PR, so I won't describe
it in this email.
I have tried to debug it and I think the problem is that we use also
server->server_hostname to compute the hash in the
ap_proxy_set_scoreboard_lb. This hash is used to find out proper
ap_scoreboard field.
It all happens in mod_proxy.c:child_init's scope.
If the "<Proxy Balancer://foobar>" has been defined, all the
BalancerMembers are initialized with the hash computed with usage of
global server->server_hostname.
Later, if the "ProxyPass /foobar/ Balancer://foobar/" has been used in
the VirtualHost, ap_proxy_initialize_worker_share is called again with
server->server_hostname set to the VirtualHost's one.
Now, the root of the error is that the scoreboard size is static (set to
proxy_lb_workers + PROXY_DYNAMIC_BALANCER_LIMIT), but it is not
incremented when ProxyPass with balancer is used in the virtualhost.
This leads to lack of space in scoreboard when Balancers are used in
multiple virtualhosts.
I think there are two possible fixes:
1) Do not use server->server_hostname when computing hash which is used
to determine right scoreboard field. I think this would fix this bug,
but I'm not sure what would happen in situations when you define 2
balancers with the same name in different virtualhosts...
On the other-side, when there is global Proxy balancer, it make sense to
use the same worker->s for all the ProxyPass in virtualhosts.
It seems that 2.4.x uses just the name of the worker to determine slot
for shared memory, so maybe it wouldn't be a problem for 2.2.x too...
Jan Kaluza
2) Increment proxy_lb_workers according to number of workers in balancer
when using "ProxyPass /foobar/ Balancer://foobar/" in the VirtualHost.
The scoreboard would have right size and ap_proxy_set_scoreboard_lb
would not fail then.
Since it's 2.2.x which should be probably stable without big changes,
I'm asking the list for more opinions... I will try to implement patch
for option 2) tomorrow and see if this really fixes the issue.
Regards,
Jan Kaluza
