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If-Modified-Since

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viggen
PostRank 10
PostRank 10
Beiträge: 6249
Registriert: 12.05.2003, 14:44

Beitrag von viggen » 22.07.2003, 07:11

googleguy hat geschrieben:Use If-Modified-Since (IMS). IMS lets your webserver tell Googlebot whether a page has changed since the last time the page was fetched. If the page hasn't changed, we can re-use the content from the last time we fetched that page. That in turn lets the bot download more pages and save bandwidth. I highly recommend that you check to see if your server is configured to support If-Modified-Since. It's an easy win for static pages, and sometimes even pages with parameters can benefit from IMS.
übersetzung hat geschrieben:Verwende "If-Modified-Since (IMS). IMS erklärt über den Webserver Googlebot ob sich eine Seite verändert hat oder nicht. Falls sich die Seite nicht verändert hat können wir die alten Daten verwenden, und Googlebot kann daher mehr spidern und auch Bandbreite sparen. Ich empfehle daher nachzuschauen ob eurer Server If-Modified-Since unterstützt.
Verwendet das jemand?
Wie genau baut man das ein?

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bugscout
PostRank 9
PostRank 9
Beiträge: 2602
Registriert: 23.06.2003, 12:24

Beitrag von bugscout » 22.07.2003, 08:52

https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

14.25 If-Modified-Since
The If-Modified-Since request-header field is used with a method to make it conditional: if the requested variant has not been modified since the time specified in this field, an entity will not be returned from the server; instead, a 304 (not modified) response will be returned without any message-body.

If-Modified-Since = "If-Modified-Since" ":" HTTP-date

An example of the field is:

If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT

A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred only if it has been modified since the date given by the If-Modified-Since header. The algorithm for determining this includes the following cases:

a) If the request would normally result in anything other than a
200 (OK) status, or if the passed If-Modified-Since date is
invalid, the response is exactly the same as for a normal GET.
A date which is later than the server's current time is
invalid.

b) If the variant has been modified since the If-Modified-Since
date, the response is exactly the same as for a normal GET.

c) If the variant has not been modified since a valid If-
Modified-Since date, the server SHOULD return a 304 (Not
Modified) response.

The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction overhead.

Note: The Range request-header field modifies the meaning of If-
Modified-Since; see section 14.35 for full details.

Note: If-Modified-Since times are interpreted by the server, whose
clock might not be synchronized with the client.

Note: When handling an If-Modified-Since header field, some
servers will use an exact date comparison function, rather than a
less-than function, for deciding whether to send a 304 (Not
Modified) response. To get best results when sending an If-
Modified-Since header field for cache validation, clients are
advised to use the exact date string received in a previous Last-
Modified header field whenever possible.

Note: If a client uses an arbitrary date in the If-Modified-Since
header instead of a date taken from the Last-Modified header for
the same request, the client should be aware of the fact that this
date is interpreted in the server's understanding of time. The
client should consider unsynchronized clocks and rounding problems
due to the different encodings of time between the client and
server. This includes the possibility of race conditions if the
document has changed between the time it was first requested and
the If-Modified-Since date of a subsequent request, and the

possibility of clock-skew-related problems if the If-Modified-
Since date is derived from the client's clock without correction
to the server's clock. Corrections for different time bases
between client and server are at best approximate due to network
latency.

The result of a request having both an If-Modified-Since header field and either an If-Match or an If-Unmodified-Since header fields is undefined by this specification.

stuijts
PostRank 8
PostRank 8
Beiträge: 968
Registriert: 27.03.2003, 15:48
Wohnort: Kerken, NRW Deutschland

Beitrag von stuijts » 22.07.2003, 10:01

Hier ist auch ein guter Doku:
https://www.mnot.net/cache_docs/

Googleguy hat hier schon in Oktober 2002 auf verwiesen...