handling the ETag

Simon Majou simon at majou.org
Thu Apr 25 13:57:22 EDT 2013

Yes thank you Dmitri
Le 25 avr. 2013 19:52, "Dmitri Zagidulin" <dzagidulin at basho.com> a écrit :

> Hi Simon,
> You are correct - setting the ETag in the Riak object header when doing a
> PUT or POST does not work (there is no way to specify or change the ETag on
> most riak clients).
> The good news is, I think you can solve your particular problem (caching
> users' web pages) without that capability. You don't really need the ETag
> of the riak _object_ in which the page is stored to match the ETag of the
> actual web page that the user's browser interacts with. (What etags are
> actually used in Riak for, is with 'If-None-Match' or 'If-Modified-Since'
> conditional HTTP semantics).
> The easiest way to implement this caching behavior is - use the Etag of
> the webpage as the key (or part of the key) for the riak object that stores
> the web page. So:
> 1) The web page is generated, and sent to the user with an etag 'abcd'.
> 2) Store that web page in Riak using the etag as the key (here, 'abcd') or
> as part of the key (something like 'your-url/index.html-abcd')
> Ignore the fact that the etag in the riak object will be something
> completely different, 'efgh'. You don't really need to use riak's etag.
> 3) When subsequent requests for that web page come in from the user's
> browser, make a GET call to Riak for the etag 'abcd' and return it if it
> exists, or else generate it & store it as usual.
> (You're probably wondering about cache expiration, and how to clean up all
> those stored web pages. Here, I would recommend using the Bitcask back end
> and setting it to auto-expire (see the Automatic Expiration section of
> http://docs.basho.com/riak/latest/tutorials/choosing-a-backend/Bitcask/). The other alternative is to keep track of the web pages and their
> expiration externally, and to issue explicit DELETE calls as part of a cron
> job.)
> Does that make sense?
> Dmitri
> On Wed, Apr 24, 2013 at 12:30 PM, Simon Majou <simon at majou.org> wrote:
>> Hello,
>> I am building a basic architecture : user / application server / riak.
>> The web pages are generated on the application server, then sent to the
>> user and finally stored (cached) in Riak. I would like the page sent to the
>> user & the page stored in Riak to have the same ETag, so new requests with
>> Etags are handled easily by forwarding them to Riak.
>> I tried to set the ETag header when doing a PUT, but it doesn't have any
>> effect.
>> So how can I do that ? Obviously I don't want to store the page in Riak
>> before sending it to the user as it would add latency.
>> Simon
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>> riak-users at lists.basho.com
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