> Vary in Squid is currently treated as an exact-match text key. So when asked > for a "gzip,deflate" variant Squid does not have enough smarts to serve the > "deflate" variant. So it MISSes and gets a fresh one, which may or may not > be gzipped, but is served gzipped to the client anyway. Right on, that makes sense. I was really trying to test gzip module vs no zipping, for clients that don't support any zipping. > When passing the second request through squid twice in a row does the reply > change from a MISS to a HIT? or stay a MISS? The second request stays a MISS. > Squid caches only one of N variants so the expected behviour is that each > new variant is a MISS but becomes a HIT on repeated duplicate requests until > a new variant pushes it out of cache. Ah, well that would sort of explain it, except I don't get a subsequent cache HIT when requesting a zipped version. So, to test all this out, I have the webserver returning either: a) a full HTML page (57580 bytes) when no Accept-Encoding header is present b) some alternate content (the Accept-Encoding header echoed back 5000 times) when Accept-Encoding is present, such that the response is a different size and dependent on the Accept-Encoding header. Then, I issue the same request headers, just modifying the Accept-Encoding header value (or excluding that header altogether). I'm using the values of "asdf" for a bogus Accept-Encoding value that shouldn't trigger gzipping, and "gzip" for when I actually want to invoke the module. To be clear, the webserver isn't zipping at all. The request headers before optionally adding an Accept-Encoding header are: GET /squid-test HTTP/1.1 User-Agent: curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3 Accept: */* Host: www.example.com Here are the response headers, all requests issued serially in the order listed here: 1. Empty Accept-Encoding header - two requests in a row, expect MISS then HIT, full content, not zipped. HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:19 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:19 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Length: 57580 X-Cache: MISS from www.example.com X-Cache-Lookup: MISS from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: keep-alive HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:19 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:19 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Length: 57580 Age: 2 X-Cache: HIT from www.example.com X-Cache-Lookup: HIT from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: keep-alive 2. Accept-Encoding: asdf header - two requests in a row, expect MISS then HIT, alternate content, not zipped. HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:35 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:35 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Length: 20006 X-Cache: MISS from www.example.com X-Cache-Lookup: MISS from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: keep-alive HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:35 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:35 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Length: 20006 Age: 2 X-Cache: HIT from www.example.com X-Cache-Lookup: HIT from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: keep-alive 3. Try no Accept-Encoding again - get a HIT, same full content from (1). HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:19 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:19 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Length: 57580 Age: 22 X-Cache: HIT from www.example.com X-Cache-Lookup: HIT from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: keep-alive 4. Now try Accept-Encoding: gzip. Two requests in a row, expect MISS then HIT, get MISSes every time. (I included the squid access log rows here to see the small zipped content length - 660 bytes.) HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:49 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:49 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Encoding: gzip X-Cache: MISS from www.example.com X-Cache-Lookup: MISS from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: close [23/Jan/2011:15:50:49 -0500] "GET http://www.example.com/squid-test HTTP/1.1" 200 660 "345 ms" "-" "curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3" TCP_MISS:ROUNDROBIN_PARENT HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:50 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:50 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Encoding: gzip X-Cache: MISS from www.example.com X-Cache-Lookup: MISS from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: close [23/Jan/2011:15:50:51 -0500] "GET http://www.example.com/squid-test HTTP/1.1" 200 660 "345 ms" "-" "curl/7.19.7 (universal-apple-darwin10.0) libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3" TCP_MISS:ROUNDROBIN_PARENT 5. Try Accept-Encoding: asdf again, get a HIT with the cached alternate content, not zipped. HTTP/1.0 200 OK Cache-Control: max-age=600 Expires: Sun, 23 Jan 2011 21:00:35 GMT Vary: Accept-Encoding Mime-Version: 1.0 Date: Sun, 23 Jan 2011 20:50:35 GMT Server: AOLserver/4.5.1 Content-Type: text/html; charset=utf-8 Content-Length: 20006 Age: 20 X-Cache: HIT from www.example.com X-Cache-Lookup: HIT from www.example.com:80 Via: 1.0 www.example.com (squid/3.1.10) Connection: keep-alive So, it looks to me like both the variants for the different Accept-Encoding values are being cached (not just one variant), except when the gzip module is invoked. I can change the behavior of the webserver to not include Vary: Accept-Encoding for content meant to be cached by squid, but that results in responses of the cached (unzipped) version even for clients who accept zipped versions, once the cache is populated by a client not requesting a zipped version, and that defeats the point of the gzip module for me because I want to gzip cached content for clients that support it. Regards, -Jon
