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Subject: Re: [Proposal] Change etag calculation
From: Adam Kocoloski <kocolosk@apache.org>
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Date: Mon, 11 Apr 2016 12:11:18 -0400
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To: dev@couchdb.apache.org

Cool. I=E2=80=99m a little confused about the MD5 for regular docs =
discussion. What=E2=80=99s the driving force behind switching away from =
revisions as ETags. Is it

1) Users can break this by setting their own revisions
2) Documents with identical bodies but different revisions should be =
cacheable

In case #1 a user operating at this level potentially breaks quite a bit =
more than the caching mechanism, doesn=E2=80=99t she? I=E2=80=99d need =
to think through the full ramifications but I=E2=80=99d love to see =
investment in the standardization of the revision generation algorithm =
as we discussed in a recent thread, and then maybe be a bit more strict =
around the revision IDs that we accept with new_edits=3Dfalse.

Case #2 also feels broken to me, we probably can=E2=80=99t be returning =
documents from a cache with the wrong revision ID.

Sorry if I=E2=80=99m missing the crux of the argument here.

Adam

> On Apr 11, 2016, at 10:43 AM, Garren Smith <garren@apache.org> wrote:
>=20
> Thanks for the feedback. For now I will proceed with getting the =
_local
> fixes then. Then we can look at a performant way of doing the md5 for
> regular docs.
>=20
> Cheers
> Garren
>=20
> On Sat, Apr 9, 2016 at 10:18 AM, Robert Newson <rnewson@apache.org> =
wrote:
>=20
>> The original patch from garren calculated the md5(body) at query =
time.
>> This was fine for just local docs since fetching then is rare.
>>=20
>> I'm +1 on the proposal and agree we need to precalculate the etag for
>> regular docs.
>>=20
>>> On 8 Apr 2016, at 19:01, Alexander Shorin <kxepal@gmail.com> wrote:
>>>=20
>>>> On Fri, Apr 8, 2016 at 8:55 PM, Mutton, James <jmutton@akamai.com>
>> wrote:
>>>> Is the proposal to calculate and store the md5 as a meta field, or =
to
>> calculate md5(_rev, body) at request time?  Doing this at request =
time
>> would be very expensive for heavily loaded servers.
>>>=20
>>> Good point and concern. This is not a new meta field, just a Etag
>>> header value. And obliviously, there should be the way to not =
generate
>>> Etag value if it eventually the same as the _rev field value (I =
think
>>> it's good idea to let them share the same algo).  Technically, this
>>> could be done by looking on what kind of edit happened: interactive =
or
>>> not.
>>>=20
>>> --
>>> ,,,^..^,,,
>>=20
>>=20