Hey guys,
I've been playing with varnish for the last few days, trying to eval it
as a squid replacement my image serving farm. I enabled it on one of the squids
friday (replacing 2 seperate squid processes on a single server), and seen
pretty awesome results:
http://boom.net/~mike/squid_vs_varnish.GIF
However, the load on my backend NFS server went up by a substantial amount. I
let it run over the weekend thinking it would smooth out once the caches were
primed, but to my dismay, this morning nfs load was still the same. After doing
some basic debugging, it appears as if the (default) varnish config is always
re-validating if-modified-since headers (when supplied by the client), thus
bypassing the local cache and hitting the origin server again. My cache objects
*never* change, so if a client supplies an if-modified-since header, I'd like
the cache to always respond '304 not modified' immediately. I've configured
squid to do this, but my vcl-fu is very weak. Before I spent more time
investigating the VCL config options, I just wanted a sanity check to make sure
it was possible to do this in varnish. At the bottom of this message i've
included a small sample of a log file i generated this morning, I could be
misreading it completely. Thanks!
ps: the above load graph is from an image server in my production pool, that
was spitting out around 150Mb/s of images at the time.
-mike
11 SessionOpen c 10.1.1.9 33194
11 ReqStart c 10.1.1.9 33194 249494004
11 RxRequestc GET
11 RxURLc /85/40/458/tn_4096253716.jpg
11 RxProtocol c HTTP/1.1
11 RxHeader c Accept: */*
11 RxHeader c Accept-Language: en-us
11 RxHeader c Accept-Encoding: gzip, deflate
11 RxHeader c If-Modified-Since: Thu, 23 Feb 2006 00:02:51 GMT
11 RxHeader c If-None-Match: 13c02df-b23-40d6af72600c0
11 RxHeader c User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT
5.1; SV1)
11 RxHeader c Host: a.pc.xyz.com:87
11 RxHeader c Connection: Keep-Alive
11 VCL_call c recv
11 VCL_return c pass
11 VCL_call c pass
11 VCL_return c pass
14 BackendClose default
14 BackendOpen b default 127.0.0.1 33977 127.0.0.1 81
14 BackendXID b 249494004
11 Backend c 14 default
14 TxRequestb GET
14 TxURLb /85/40/458/tn_4096253716.jpg
14 TxProtocol b HTTP/1.1
14 TxHeader b Accept: */*
14 TxHeader b Accept-Language: en-us
14 TxHeader b Accept-Encoding: gzip, deflate
14 TxHeader b User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT
5.1; SV1)
14 TxHeader b Host: a.pc.xyz.com:87
14 TxHeader b X-Varnish: 249494004
14 TxHeader b X-Forwarded-for: 10.1.1.9
14 RxProtocol b HTTP/1.1
14 RxStatus b 200
14 RxResponse b OK
14 RxHeader b Date: Mon, 02 Jul 2007 17:59:03 GMT
14 RxHeader b Server: Apache
14 RxHeader b Last-Modified: Thu, 23 Feb 2006 00:02:51 GMT
14 RxHeader b ETag: 13c02df-b23-40d6af72600c0
14 RxHeader b Accept-Ranges: bytes
14 RxHeader b Content-Length: 2851
14 RxHeader b Content-Type: image/jpeg
11 ObjProtocol c HTTP/1.1
11 ObjStatusc 200
11 ObjResponse c OK
11 ObjHeaderc Date: Mon, 02 Jul 2007 17:59:03 GMT
11 ObjHeaderc Server: Apache
11 ObjHeaderc Last-Modified: Thu, 23 Feb 2006 00:02:51 GMT
11 ObjHeaderc ETag: 13c02df-b23-40d6af72600c0
11 ObjHeaderc Content-Type: image/jpeg
11 ObjHeaderc Content-Length: 2851
14 BackendReuse b default
11 TTL c 249494004 RFC 3600 1183399143 1183399143 0 0 0
11 VCL_call c fetch
11 VCL_return c insert
11 Length c 0
11 TxProtocol c HTTP/1.1
11 TxStatus c 304
11 TxResponse c Not Modified
11 TxHeader c Date: Mon, 02 Jul 2007 17:59:03 GMT
11 TxHeader c Via: 1.1 varnish
11 TxHeader c X-Varnish: 249494004
11 TxHeader c Last-Modified: Thu, 23 Feb 2006 00:02:51 GMT
11 ReqEnd c 249494004 1183399143.654401000 1183399143.656763000
0.43000 0.002308000 0.54000
0 StatAddr 10.1.1.9 0 579 116 68 0 0 13 18505 6270
11 SessionOpen c 10.1.1.9 61746
11 ReqStart c 10.1.1.9 61746 249494005
11 RxRequestc GET
11 RxURLc /85/40/458/tn_4096253716.jpg
11 RxProtocol c HTTP/1.1
11 RxHeader c Accept: */*
11 RxHeader c Accept-Language: en-us
11 RxHeader c Accept-Encoding: gzip, deflate
11 RxHeader c If-Modified-Since: Thu, 23 Feb 2006 00:02:51 GMT
11 RxHeader c If-None-Match: 13c02df-b23-40d6af72600c0
11 RxHeader c User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT
5.1; SV1)
11 RxHeader c Host: a.pc.xyz.com:87
11 RxHeader c Connection: Keep-Alive
11 VCL_call c recv
11 VCL_return c pass
11 VCL_call c pass
11 VCL_return c pass
14 BackendClose b default
14 BackendOpen b default
