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http://issues.apache.org/bugzilla/show_bug.cgi?id=38227 ------- Additional Comments From [EMAIL PROTECTED] 2006-04-13 15:54 ------- Folks, I don't know if my previous followup on this bug was read or not, or if people are already looking at it. Without feedback, I can't tell if I should keep pursuing this, follow up with more details, etc. I can understand somebody telling me "No, we know this isn't the problem" but I'm not hearing anything. Without feedback I'm stuck not knowing if this is a bug or a fatal misunderstanding on my part. Given httpd 2.2.1 and the following settings: Server Version: Apache/2.2.1 (Unix) DAV/2 mod_ssl/2.2.1 OpenSSL/0.9.7a Server Built: Apr 6 2006 00:22:26 Module Magic Number: 20051115:1 Hostname/port: server.mydomain.org:80 Timeouts: connection: 300 keep-alive: 300 MPM Name: Worker MPM Information: Max Daemons: 2 Threaded: yes Forked: yes Server Architecture: 32-bit Server Root: /highwire/server/apache Config File: -c/-C directives Server Built With: -D APACHE_MPM_DIR="server/mpm/worker" -D APR_HAS_SENDFILE -D APR_HAS_MMAP -D APR_HAVE_IPV6 (IPv4-mapped addresses enabled) -D APR_USE_SYSVSEM_SERIALIZE -D SINGLE_LISTEN_UNSERIALIZED_ACCEPT -D APR_HAS_OTHER_CHILD -D AP_HAVE_RELIABLE_PIPED_LOGS -D HTTPD_ROOT="/usr/local/apache/2.2.1" -D SUEXEC_BIN="/usr/local/apache/2.2.1/bin/suexec" -D DEFAULT_ERRORLOG="logs/error_log" -D AP_TYPES_CONFIG_FILE="conf/mime.types" -D SERVER_CONFIG_FILE="conf/httpd.conf" It appears as though the mod_proxy pool of connections is not being consistently reused when the balancer is used. Given the configuration: ServerLimit 2 ThreadsPerChild 10 <Proxy balancer://tomcat> BalancerMember ajp://server.mydomain.org:8009 route=server.mydomain.org </Proxy> <VirtualHost vhost.mydomain.org:80> ServerName vhost.mydomain.org RewriteEngine on RewriteCond %{ENV:HTTPD_BASE}/logs/myapp.pause -f RewriteRule .* - [forbidden,last] DocumentRoot vhosts/myapp/htdocs RewriteRule ^(/+test(?:/.*)?)$ /myapp$1 [env=internal:yes] RewriteCond %{ENV:internal} =yes RewriteRule ^(/+myapp/.*) $1 [passthrough,last] RewriteRule ^/+myapp/(.*) /$1 [redirect=permanent,last] ProxyPass /myapp balancer://tomcat/myapp stickysession=JSESSIONID nofailover=on ProxyPassReverse / http://vhost.mydomain.org/myapp/ ProxyPassReverseCookiePath /myapp/ / </VirtualHost> My understanding of the documentation http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#proxypass is that, with the above ServerLimit and ThreadPerChild limit, we should never see more than 20 connections form between Apache and any one BalancerMember target (2 servers x 10 threads = 20 total threads). On startup, we see zero connections between Apache and Tomcat: ; netstat -t | tr -s " " | egrep "^tcp.*:8009 ESTABLISHED" ; I make one request, and see one connection form: ; ab -n 1 http://vhost.mydomain.org/test ; netstat -t | tr -s " " | egrep "^tcp.*:8009 ESTABLISHED" tcp 0 0 server.mydomain.org:59165 server.mydomain.org:8009 ESTABLISHED Now what happens if I make 20 concurrent requests? What I would expect to see is up to 20 connections established, and no more. ; ab -c 20 -n 20 http://vhost.mydomain.org/test ; netstat -t | tr -s " " | egrep "^tcp.*:8009 ESTABLISHED"|wc -l 21 If I make another 20 connections, I see the connections more than double: ; ab -c 20 -n 20 http://vhost.mydomain.org/test ; netstat -t | tr -s " " | egrep "^tcp.*:8009 ESTABLISHED"|wc -l 44 Now look what happens when I plug in min/smax/max settings into the BalancerMember directive. These are settings which I think the documentation indicates are the defaults, given my configuration above: <Proxy balancer://tomcat> BalancerMember ajp://server.mydomain.org:8009 route=server.mydomain.org min=0 smax=10 max=10 </Proxy> After an apache restart, we have no connections, I make a bunch of requests, and see 20 connections, and never more than that. Even when I make 50 concurrent requests, Apache simply queues and processes as it should: ; netstat -t | tr -s " " | egrep "^tcp.*:8009 ESTABLISHED"|wc -l 0 ; ab -c 20 -n 20 http://vhost.mydomain.org/test ; netstat -t | tr -s " " | egrep "^tcp.*:8009 ESTABLISHED"|wc -l 20 ; ab -c 50 -n 50 http://vhost.mydomain.org/test ; netstat -t | tr -s " " | egrep "^tcp.*:8009 ESTABLISHED"|wc -l 20 If we activate the balancer, and the balancer has only one Tomcat target as in this case, shouldn't it should still be obeying the same limits as defined in the configuration. Otherwise we have a situation where the number of proxy connections is unbounded, right? Say Apache is configured to serve no more than 1024 requests at any one moment in time, and we wanted to balance load between two Tomcat servers. What we'd probably do is set up two Tomcat servers which are each configured to accept 1024 requests, but we would expect to see apache balancer send ~512 requests to each Tomcat server. What we would *not* expect to see is Apache opening more connections to a Tomcat server than Apache itself is configured to serve at any one time. In summary, it appears to be a bug to have to declare min/smax/max values which are the same as the defaults per the documentation, without which the number of connections opened appears to be unbounded. My examination of the code led me to believe that the source of the problem is that the BalancerMember worker is not getting its hmax value properly initialized, and that it is therefore bypassing the pool of reusable connections when it is acquiring connections (proxy_util.c:1758, in ap_proxy_acquire_connection). If I add the patch I submitted in comment #14 and remove the min/smax/max directives, I see the behavior I am expecting -- Apache never opens more than 20 connections in all to its Tomcat server. Looking at svn.apache.org, I see that initialization was actually removed in a previous version, though the comments do not explain why it is not appropriate to initialize the balancer worker: http://svn.apache.org/viewcvs.cgi/httpd/httpd/trunk/modules/proxy/proxy_balancer.c?rev=105347&r1=105320&r2=105347 The only reason I can think of to have the current behavior is that somehow the dynamic of balancing between multiple backend servers is expected to be able to handle more connections -- but it just doesn't make sense to me that it would ever be normal for Apache to open more connections to any one backend server than Apache can serve itself. If this isn't considered a bug, I'd very much appreciate it if someone would point out the reason. Thank you for your time, Jim -- Configure bugmail: http://issues.apache.org/bugzilla/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug, or are watching the assignee. --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
