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Re: [indexeddb] Count property on IDBCursor

From: Jonas Sicking <jonas@sicking.cc>
Date: Thu, 23 Jun 2011 19:41:38 -0700
Message-ID: <BANLkTimw6kBhhauhuYSndD5i2sr4hu+A8A@mail.gmail.com>
To: Israel Hilerio <israelh@microsoft.com>
Cc: "public-webapps@w3.org" <public-webapps@w3.org>
On Thu, Jun 23, 2011 at 5:34 PM, Israel Hilerio <israelh@microsoft.com> wrote:
> Is there a reason why we donít have a count or number of records property on
> IDBCursor?† Pablo told me that we used to have one.† What happened to it?
> It will be great to bring it back.

The problem is that counting the number of records in a given range
can be a very expensive operation. There are various database
implementations out there that lets you get an approximate count for a
given key range, but that isn't good enough if since we want
interoperability across implementations.

Since getting an exact count is a pretty expensive operation
generally, we don't want to force implementations to always calculate
the count every time a cursor is created. Hence getting the count
would have to be an asynchronous operation, which would look pretty
awkward as an API on the cursor object I think.

What could possibly make more sense is to add

IDBRequest count(in IDBKeyRange range)

on IDBObjectStore and IDBIndex. My main concern with that is that
while that seems like a pretty cheap operation, in the order of get(),
it might be as slow as creating a cursor and iterating each entry
while increasing a counter (minus the overhead of crossing between C++
and JS for every callback). But maybe that's ok.

/ Jonas
Received on Friday, 24 June 2011 02:42:44 UTC

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