Network Working Group I. Cooper Request for Comments: 3143 Equinix, Inc. Category: Informational J. Dilley Akamai Technologies, Inc. June 2001 Known HTTP Proxy/Caching Problems Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2001). All Rights Reserved.
AbstractThis document catalogs a number of known problems with World Wide Web (WWW) (caching) proxies and cache servers. The goal of the document is to provide a discussion of the problems and proposed workarounds, and ultimately to improve conditions by illustrating problems. The construction of this document is a joint effort of the Web caching community. 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Problem Template . . . . . . . . . . . . . . . . . . . . . . 2 2. Known Problems . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Known Specification Problems . . . . . . . . . . . . . . . . 5 2.1.1 Vary header is underspecified and/or misleading . . . . . . 5 2.1.2 Client Chaining Loses Valuable Length Meta-Data . . . . . . 9 2.2 Known Architectural Problems . . . . . . . . . . . . . . . . 10 2.2.1 Interception proxies break client cache directives . . . . . 10 2.2.2 Interception proxies prevent introduction of new HTTP methods . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.3 Interception proxies break IP address-based authentication . 12 2.2.4 Caching proxy peer selection in heterogeneous networks . . . 13 2.2.5 ICP Performance . . . . . . . . . . . . . . . . . . . . . . 15 2.2.6 Caching proxy meshes can break HTTP serialization of content 16 2.3 Known Implementation Problems . . . . . . . . . . . . . . . 17 2.3.1 User agent/proxy failover . . . . . . . . . . . . . . . . . 17 2.3.2 Some servers send bad Content-Length headers for files that contain CR . . . . . . . . . . . . . . . . . . . . . . . 18
3. Security Considerations . . . . . . . . . . . . . . . . . . 18 References . . . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 20 A. Archived Known Problems . . . . . . . . . . . . . . . . . . 21 A.1 Architectural . . . . . . . . . . . . . . . . . . . . . . . 21 A.1.1 Cannot specify multiple URIs for replicated resources . . . 21 A.1.2 Replica distance is unknown . . . . . . . . . . . . . . . . 22 A.1.3 Proxy resource location . . . . . . . . . . . . . . . . . . 23 A.2 Implementation . . . . . . . . . . . . . . . . . . . . . . . 23 A.2.1 Use of Cache-Control headers . . . . . . . . . . . . . . . . 23 A.2.2 Lack of HTTP/1.1 compliance for caching proxies . . . . . . 24 A.2.3 ETag support . . . . . . . . . . . . . . . . . . . . . . . . 25 A.2.4 Servers and content should be optimized for caching . . . . 26 A.3 Administration . . . . . . . . . . . . . . . . . . . . . . . 27 A.3.1 Lack of fine-grained, standardized hierarchy controls . . . 27 A.3.2 Proxy/Server exhaustive log format standard for analysis . . 27 A.3.3 Trace log timestamps . . . . . . . . . . . . . . . . . . . . 28 A.3.4 Exchange format for log summaries . . . . . . . . . . . . . 29 Full Copyright Statement . . . . . . . . . . . . . . . . . . 32 2]. No individual or organization has complete knowledge of the known problems in Web caching, and the editors are grateful to the contributors to this document. RFC2525  which helped define an initial format for this known problems list. The template format is summarized in the following table and described in more detail below. Name: short, descriptive name of the problem (3-5 words) Classification: classifies the problem: performance, security, etc Description: describes the problem succinctly Significance: magnitude of problem, environments where it exists Implications: the impact of the problem on systems and networks See Also: a reference to a related known problem Indications: states how to detect the presence of this problem
Solution(s): describe the solution(s) to this problem, if any Workaround: practical workaround for the problem References: information about the problem or solution Contact: contact name and email address for this section Name A short, descriptive, name (3-5 words) name associated with the problem. Classification Problems are grouped into categories of similar problems for ease of reading of this memo. Choose the category that best describes the problem. The suggested categories include three general categories and several more specific categories. * Architecture: the fundamental design is incomplete, or incorrect * Specification: the spec is ambiguous, incomplete, or incorrect. * Implementation: the implementation of the spec is incorrect. * Performance: perceived page response at the client is excessive; network bandwidth consumption is excessive; demand on origin or proxy servers exceed reasonable bounds. * Administration: care and feeding of caches is, or causes, a problem. * Security: privacy, integrity, or authentication concerns. Description A definition of the problem, succinct but including necessary background information. Significance (High, Medium, Low) May include a brief summary of the environments for which the problem is significant. Implications Why the problem is viewed as a problem. What inappropriate behavior results from it? This section should substantiate the magnitude of any problem indicated with High significance. See Also Optional. List of other known problems that are related to this one.
Indications How to detect the presence of the problem. This may include references to one or more substantiating documents that demonstrate the problem. This should include the network configuration that led to the problem such that it can be reproduced. Problems that are not reproducible will not appear in this memo. Solution(s) Solutions that permanently fix the problem, if such are known. For example, what version of the software does not exhibit the problem? Indicate if the solution is accepted by the community, one of several solutions pending agreement, or open possibly with experimental solutions. Workaround Practical workaround if no solution is available or usable. The workaround should have sufficient detail for someone experiencing the problem to get around it. References References to related information in technical publications or on the web. Where can someone interested in learning more go to find out more about this problem, its solution, or workarounds? Contact Contact name and email address of the person who supplied the information for this section. The editors are listed as contacts for anonymous submissions. Appendix A since they discuss issues where resolution primarily involves education rather than protocol work. A full list of the problems is available in the table of contents.
RFC 2616 says: The Vary header field can be used to express the parameters the server uses to select a representation that is subject to server-driven negotiation. One might expect that this mechanism is useful in general for extensions that change the response message based on some aspects of the request. However, that is not true. During the design of the HTTP delta encoding specification it was realized that an HTTP/1.1 proxy that does not understand delta encoding might cache a delta-encoded response and then later deliver it to a non-delta-capable client, unless the extension included some mechanism to prevent this. Initially, it was thought that Vary would suffice, but the following scenario proves this wrong. NOTE: It is likely that other scenarios exhibiting the same basic problem with "Vary" could be devised, without reference to delta encoding. This is simply a concrete scenario used to explain the problem. A complete description of the IM and A-IM headers may be found in the "Delta encoding in HTTP" specification. For the purpose of this problem description, the relevant details are: 1. The concept of an "instance manipulation" is introduced. In some ways, this is similar to a content-coding, but there are differences. One example of an instance manipulation name is "vcdiff". 2. A client signals its willingness to accept one or more instance-manipulations using the A-IM header.
3. A server indicates which instance-manipulations are used to encode the body of a response using the IM header. 4. Existing implementations will ignore the A-IM and IM headers, following the usual HTTP rules for handling unknown headers. 5. Responses encoded with an instance-manipulation are sent using the (proposed) 226 status code, "IM Used". 6. In response to a conditional request that carries an IM header, if the request-URI has been modified then a server may transmit a compact encoding of the modifications using a delta-encoding instead of a status-200 response. The encoded response cannot be understood by an implementation that does not support delta encodings. This summary omits many details. Suppose client A sends this request via proxy P: GET http://example.com/foo.html HTTP/1.1 Host: example.com If-None-Match: "abc" A-IM: vcdiff and the origin server returns, via P, this response: HTTP/1.1 226 IM Used Etag: "def" Date: Wed, 19 Apr 2000 18:46:13 GMT IM: vcdiff Cache-Control: max-age-60 Vary: A-IM, If-None-Match the body of which is a delta-encoded response (it encodes the difference between the Etag "abc" instance of foo.html, and the "def" instance). Assume that P stores this response in its cache, and that P does not understand the vcdiff encoding. Later, client B, also ignorant of delta-encoding, sends this request via P: GET http://example.com/foo.html HTTP/1.1 Host: example.com What can P do now? According to the specification for the Vary header in RFC2616,
The Vary field value indicates the set of request-header fields that fully determines, while the response is fresh, whether a cache is permitted to use the response to reply to a subsequent request without revalidation. Implicitly, however, the cache would be allowed to use the stored response in response to client B WITH "revalidation". This is the potential bug. An obvious implementation of the proxy would send this request to test whether its cache entry is fresh (i.e., to revalidate the entry): GET /foo.html HTTP/1.1 Host: example.com If-None-Match: "def" That is, the proxy simply forwards the new request, after doing the usual transformation on the URL and tacking on the "obvious" If-None-Match header. If the origin server's Etag for the current instance is still "def", it would naturally respond: HTTP/1.1 304 Not Modified Etag: "def" Date: Wed, 19 Apr 2000 18:46:14 GMT thus telling the proxy P that it can use its stored response. But this cache response actually involves a delta-encoding that would not be sensible to client B, signaled by a header field that would be ignored by B, and so the client displays garbage. The problem here is that the original request (from client A) generated a response that is not sensible to client B, not merely one that is not "the appropriate representation" (as the result of server-driven negotiation). One might argue that the proxy P shouldn't be storing status-226 responses in the first place. True in theory, perhaps, but unfortunately RFC2616, section 13.4, says: A response received with any [status code other than 200, 203, 206, 300, 301 or 410] MUST NOT be returned in a reply to a subsequent request unless there are cache-control directives or another header(s) that explicitly allow it. For example, these
include the following: an Expires header (section 14.21); a "max-age", "s-maxage", "must-revalidate", "proxy-revalidate", "public" or "private" cache-control directive (section 14.9). In other words, the specification allows caching of responses with yet-to-be-defined status codes if the response carries a plausible Cache-Control directive. So unless we ban servers implementing this kind of extension from using these Cache-Control directives at all, the Vary header just won't work. Significance Medium Implications Certain plausible extensions to the HTTP/1.1 protocol might not interoperate correctly with older HTTP/1.1 caches, if the extensions depend on an interpretation of Vary that is not the same as is used by the cache implementer. This would have the effect either of causing hard-to-debug cache transparency failures, or of discouraging the deployment of such extensions, or of encouraging the implementers of such extensions to disable caching entirely. Indications The problem is visible when hand-simulating plausible message exchanges, especially when using the proposed delta encoding extension. It probably has not been visible in practice yet. Solution(s) 1. Section 13.4 of the HTTP/1.1 specification should probably be changed to prohibit caching of responses with status codes that the cache doesn't understand, whether or not they include Expires headers and the like. (It might require some care to define what "understands" means, leaving room for future extensions with new status codes.) The behavior in this case needs to be defined as equivalent to "Cache-Control: no-store" rather than "no-cache", since the latter allows revalidation. Possibly the specification of Vary should require that it be treated as "Cache-Control: no-store" whenever the status code is unknown - that should solve the problem in the scenario given here.
2. Designers of HTTP/1.1 extensions should consider using mechanisms other than Vary to prevent false caching. It is not clear whether the Vary mechanism is widely implemented in caches; if not, this favors solution #1. Workaround A cache could treat the presence of a Vary header in a response as an implicit "Cache-control: no-store", except for "known" status codes, even though this is not required by RFC 2616. This would avoid any transparency failures. "Known status codes" for basic HTTP/1.1 caches probably include: 200, 203, 206, 300, 301, 410 (although this list should be re-evaluated in light of the problem discussed here). References See  for the specification of the delta encoding extension, as well as for an example of the use of a Cache-Control extension instead of "Vary." Contact Jeff Mogul <firstname.lastname@example.org> 3] implementations are prohibited from sending Content- Length headers with any message whose body has been Transfer- Encoded. Because 1.0 clients cannot accept chunked Transfer- Encodings, receiving 1.1 implementations must forward the body to 1.0 clients must do so without the benefit of information that was discarded earlier in the chain. Significance Low Implications Lacking either a chunked transfer encoding or Content-Length indication creates negative performance implications for how the proxy must forward the message body.
In the case of response bodies, the server may either forward the response while closing the connection to indicate the end of the response or must utilize store and forward semantics to buffer the entire response in order to calculate a Content-Length. The former option defeats the performance benefits of persistent connections in HTTP/1.1 (and their Keep-Alive cousin in HTTP/1.0) as well as creating some ambiguously lengthed responses. The latter store and forward option may not even be feasible given the size of the resource and it will always introduce increased latency. Request bodies must undertake the store and forward process as 1.0 request bodies must be delimited by Content-Length headers. As with response bodies this may place unacceptable resource constraints on the proxy and the request may not be able to be satisfied. Indications The lack of HTTP/1.0 style persistent connections between 1.0 clients and 1.1 proxies, only when accessing 1.1 servers, is a strong indication of this problem. Solution(s) An HTTP specification clarification that would allow origin known identity document Content-Lengths to be carried end to end would alleviate this issue. Workaround None. Contact Patrick McManus <mcmanus@AppliedTheory.com> 3] is designed for the user agent to be aware if it is connected to an origin server or to a proxy. User agents believing they are transacting with an origin server but which are
really in a connection with an interception proxy may fail to send critical cache-control information they would have otherwise included in their request. Significance High Implications Clients may receive data that is not synchronized with the origin even when they request an end to end refresh, because of the lack of inclusion of either a "Cache-control: no-cache" or "must- revalidate" header. These headers have no impact on origin server behavior so may not be included by the browser if it believes it is connected to that resource. Other related data implications are possible as well. For instance, data security may be compromised by the lack of inclusion of "private" or "no-store" clauses of the Cache-control header under similar conditions. Indications Easily detected by placing fresh (un-expired) content on a caching proxy while changing the authoritative copy, then requesting an end-to-end reload of the data through a proxy in both interception and explicit modes. Solution(s) Eliminate the need for interception proxies and IP spoofing, which will return correct context awareness to the client. Workaround Include relevant Cache-Control directives in every request at the cost of increased bandwidth and CPU requirements. Contact Patrick McManus <mcmanus@AppliedTheory.com>
server. An interception proxy that hijacks requests which include new methods destined for servers that have implemented those methods creates a de-facto firewall where none may be intended. Significance Medium within interception proxy environments. Implications Renders new compliant applications useless unless modifications are made to proxy software. Because new methods are not required to be globally standardized it is impossible to keep up to date in the general case. Solution(s) Eliminate the need for interception proxies. A client receiving a 501 in a traditional HTTP environment may either choose to repeat the request to the origin server directly, or perhaps be configured to use a different proxy. Workaround Level 5 switches (sometimes called Level 7 or application layer switches) can be used to keep HTTP traffic with unknown methods out of the proxy. However, these devices have heavy buffering responsibilities, still require TCP sequence number spoofing, and do not interact well with persistent connections. The HTTP/1.1 specification allows a proxy to switch over to tunnel mode when it receives a request with a method or HTTP version it does not understand how to handle. Contact Patrick McManus <mcmanus@AppliedTheory.com> Henrik Nordstrom <email@example.com> (HTTP/1.1 clarification)
knowledge of the client/user. This breaks such authentication mechanisms and prohibits otherwise allowed clients access to the servers. Significance Medium Implications Creates end user confusion and frustration. Indications Users may start to see refused connections to servers after interception proxies are deployed. Solution(s) Use user-based authentication instead of (IP) address-based authentication. Workaround Using IP filters at the intercepting device (L4 switch) and bypass all requests to such servers concerned. Contact Keith K. Chau <firstname.lastname@example.org> 4] based caching proxy peer selection in networks with large variance in latency and bandwidth between peers can lead to non- optimal peer selection. For example take Proxy C with two siblings, Sib1 and Sib2, and the following network topology (summarized). * Cache C's link to Sib1, 2 Mbit/sec with 300 msec latency * Cache C's link to Sib2, 64 Kbit/sec with 10 msec latency. ICP does not work well in this context. If a user submits a request to Proxy C for page P that results in a miss, C will send an ICP request to Sib1 and Sib2. Assume both siblings have the
requested object P. The ICP_HIT reply will always come from Sib2 before Sib1. However, it is clear that the retrieval of large objects will be faster from Sib1, rather than Sib2. The problem is more complex because Sib1 and Sib2 can't have a 100% hit ratio. With a hit rate of 10%, it is more efficient to use Sib1 with resources larger than 48K. The best choice depends on at least the hit rate and link characteristics; maybe other parameters as well. Significance Medium Implications By using the first peer to respond, peer selection algorithms are not optimizing retrieval latency to end users. Furthermore they are causing more work for the high-latency peer since it must respond to such requests but will never be chosen to serve content if the lower latency peer has a copy. Indications Inherent in design of ICP v1, ICP v2, and any cache mesh protocol that selects peers based upon first response. This problem is not exhibited by cache digest or other protocols which (attempt to) maintain knowledge of peer contents and only hit peers that are believed to have a copy of the requested page. Solution(s) This problem is architectural with the peer selection protocols. Workaround Cache mesh design when using such a protocol should be done in such a way that there is not a high latency variance among peers. In the example presented in the above description the high latency high bandwidth peer could be used as a parent, but should not be used as a sibling. Contact Ivan Lovric <email@example.com> John Dilley <firstname.lastname@example.org>
4] exhibits O(n^2) scaling properties, where n is the number of participating peer proxies. This can lead ICP traffic to dominate HTTP traffic within a network. Significance Medium Implications If a proxy has many ICP peers the bandwidth demand of ICP can be excessive. System managers must carefully regulate ICP peering. ICP also leads proxies to become homogeneous in what they serve; if your proxy does not have a document it is unlikely your peers will have it either. Therefore, ICP traffic requests are largely unable to locate a local copy of an object (see ). Indications Inherent in design of ICP v1, ICP v2. Solution(s) This problem is architectural - protocol redesign or replacement is required to solve it if ICP is to continue to be used. Workaround Implementation workarounds exist, for example to turn off use of ICP, to carefully regulate peering, or to use another mechanism if available, such as cache digests. A cache digest protocol shares a summary of cache contents using a Bloom Filter technique. This allows a cache to estimate whether a peer has a document. Filters are updated regularly but are not always up-to-date so cannot help when a spike in popularity occurs. They also increase traffic but not as much as ICP. Proxy clustering protocols organize proxies into a mesh provide another alternative solution. There is ongoing research on this topic. Contact John Dilley <email@example.com>
3] advises that caches MAY store partial responses. Indications Count the number of bytes in the message body and compare to the Content-length value. If they differ the server exhibits this problem. Solutions Upgrade or replace the buggy server. Workaround Some browsers and proxies use one TCP connection per object and ignore the Content-Length. The document end of file is identified by the close of the TCP socket. Contact Duane Wessels <firstname.lastname@example.org>
References  Paxson, V., Allman, M., Dawson, S., Fenner, W., Griner, J., Heavens, I., Lahey, K., Semke, J. and B. Volz, "Known TCP Implementation Problems", RFC 2525, March 1999.  Cooper, I., Melve, I. and G. Tomlinson, "Internet Web Replication and Caching Taxonomy", RFC 3040, January 2001.  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.  Wessels, D. and K. Claffy, "Internet Cache Protocol (ICP), Version 2", RFC 2186, September 1997.  Davison, B., "Web Traffic Logs: An Imperfect Resource for Evaluation", in Proceedings of the Ninth Annual Conference of the Internet Society (INET'99), July 1999.  Melve, I., "Relation Analysis, Cache Meshes", in Proceedings of the 3rd International WWW Caching Workshop, June 1998, <http://wwwcache.ja.net/events/workshop/29/magicnumber.html>.  Krishnamurthy, B. and M. Arlett, "PRO-COW: Protocol Compliance on the Web", AT&T Labs Technical Report #990803-05-TM, August 1999, <http://www.research.att.com/~bala/papers/procow-1.ps.gz>.  Netscape, Inc., "Navigator Proxy Auto-Config File Format", March 1996, http://home.netscape.com/eng/mozilla/2.0/relnotes/demo/proxy- live.html  Mogul, J., Krishnamurthy, B., Douglis, F., Feldmann, A., Goland, Y., van Hoff, A. and D. Hellerstein, "HTTP Delta in HTTP", Work in Progress.
Authors' Addresses Ian Cooper Equinix, Inc. 2450 Bayshore Parkway Mountain View, CA 94043 USA Phone: +1 650 316 6065 EMail: email@example.com John Dilley Akamai Technologies, Inc. 1400 Fashion Island Blvd Suite 703 San Mateo, CA 94404 USA Phone: +1 650 627 5244 EMail: firstname.lastname@example.org
Section 2.2.5).) Contact Daniel LaLiberte <email@example.com>
Description Many (if not most) implementations incorrectly interpret Cache- Control response headers. Significance High Implications Cache-Control headers will be spurned by end users if there are conflicting or non-standard implementations. Indications - Solution(s) Work with vendors and others to assure proper application Workaround None. Contact Mark Nottingham <firstname.lastname@example.org>
Indications There is no currently known compliance test being used. There is work underway to quantify how closely servers comply with the current specification. A joint technical report between AT&T and HP Labs  describes the compliance testing. This report examines how well each of a set of top traffic-producing sites support certain HTTP/1.1 features. The Measurement Factory (formerly IRCache) is working to develop protocol compliance testing software. Running such a conformance test suite against caching proxy products would measure compliance and ultimately would help assure they comply to the specification. Solution(s) Testing should commence and be reported in an open industry forum. Proxy implementations should conform to the specification. Workaround There is no workaround for non-compliance. Contact Mark Nottingham <email@example.com> Duane Wessels <firstname.lastname@example.org>
Solution(s) Work with vendors to implement ETags; work for better validation protocols. Workaround Use Last-Modified/If-Modified-Since validation. Contact Mark Nottingham <email@example.com>
Description Most proxy or origin server logs used for characterization or evaluation do not provide sufficient detail to determine cacheability of responses. Significance Low (for operationality; high significance for research efforts) Implications Characterizations and simulations are based on non-representative workloads. See Also W3C Web Characterization Activity, since they are also concerned with collecting high quality logs and building characterizations from them. Indications - Solution(s) To properly clean and to accurately determine cacheability of responses, a complete log is required (including all request headers as well as all response headers such as "User-agent" [for removal of spiders] and "Expires", "max-age", "Set-cookie", "no- cache", etc.) Workaround - References See "Web Traffic Logs: An Imperfect Resource for Evaluation" for some discussion of this. Contact Brian D. Davison <firstname.lastname@example.org> Terence Kelly <email@example.com>
Description Some proxies/servers log requests without sufficient timing detail. Millisecond resolution is often too small to preserve request ordering and either the servers should record request reception time in addition to completion time, or elapsed time plus either one. Significance Low (for operationality; medium significance for research efforts) Implications Characterization and simulation fidelity is improved with accurate timing and ordering information. Since logs are generally written in order of request completion, these logs cannot be re-played without knowing request generation times and reordering accordingly. See Also - Indications Timestamps can be identical for multiple entries (when only millisecond resolution is used). Request orderings can be jumbled when clients open additional connections for embedded objects while still receiving the container object. Solution(s) Since request completion time is common (e.g., Squid), recommend continuing to use it (with microsecond resolution if possible) plus recording elapsed time since request reception. Workaround - References See "Web Traffic Logs: An Imperfect Resource for Evaluation" for some discussion of this. Contact Brian D. Davison <firstname.lastname@example.org>
Description Although we have (more or less) a standard log file format for proxies (plain vanilla Common Logfile and Squid), there isn't a commonly accepted format for summaries of those log files. Summaries could be generated by the cache itself, or by post- processing existing log file formats such as Squid's. Significance High, since it means that each log file summarizing/analysis tool is essentially reinventing the wheel (un-necessary repetition of code), and the cost of processing a large number of large log files through a variety of analysis tools is (again for no good reason) excessive. Implications In order to perform a meaningful analysis (e.g., to measure performance in relation to loading/configuration over time) the access logs from multiple busy caches, it's often necessary to run first one tool then another, each against the entire log file (or a significantly large subset of the log). With log files running into hundreds of MB even after compression (for a cache dealing with millions of transactions per day) this is a non-trivial task. See Also IP packet/header sniffing - it may be that individual transactions are at a level of granularity which simply isn't sensible to be attempting on extremely busy caches. There may also be legal implications in some countries, e.g., if this analysis identifies individuals. Indications Disks/memory full(!) Stats (using multiple programs) take too long to run. Stats crunching must be distributed out to multiple machines because of its high computational cost. Solution(s) Have the proxy produce a standardized summary of its activity either automatically or via an external (e.g., third party) tool, in a commonly agreed format. The format could be something like XML or the Extended Common Logfile, but the format and contents are subjects for discussion. Ideally this approach would permit individual cache server products to supply subsets of the possible summary info, since it may not be feasible for all servers to provide all of the information which people would like to see.
Workaround Devise a private summary format for your own personal use - but this complicates or even precludes the exchange of summary info with other interested parties. References See the web pages for the commonly used cache stats analysis programs, e.g., Calamaris, squidtimes, squidclients, etc. Contact Martin Hamilton <email@example.com>
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