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RE: [IndexedDB] IDBObjectStore.delete should accept a KeyRange

From: Israel Hilerio <israelh@microsoft.com>
Date: Thu, 27 Oct 2011 16:33:38 +0000
To: Jonas Sicking <jonas@sicking.cc>
CC: Joshua Bell <jsbell@chromium.org>, "public-webapps@w3.org" <public-webapps@w3.org>, Adam Herchenroether <aherchen@microsoft.com>, "Victor Ngo" <vicngo@microsoft.com>, Jim Wordelman <jaword@microsoft.com>
Message-ID: <F695AF7AA77CC745A271AD0F61BBC61E3F51DFAD@TK5EX14MBXC115.redmond.corp.microsoft.com>
On Wednesday, October 26, 2011 6:38 PM, Jonas Sicking wrote:
> On Wed, Oct 26, 2011 at 11:31 AM, Israel Hilerio <israelh@microsoft.com>
> wrote:
> > On Wednesday, October 26, 2011 9:35 AM, Joshua Bell wrote:
> >>On Tue, Oct 25, 2011 at 4:50 PM, Israel Hilerio <israelh@microsoft.com>
> wrote:
> >>>On Monday, October 24, 2011 7:40 PM, Jonas Sicking wrote:
> >>>>
> >>>> While I was there it did occur to me that the fact that the .delete
> >>>> function "returns" (through request.result in the async API)
> >>>> true/false depending on if any records were removed or not might be
> bad for performance.
> >>>>
> >>>> I suspect that this highly depends on the implementation and that
> >>>> in some implementations knowing if records were deleted will be
> >>>> free and in others it will be as costly as a .count() and then a
> >>>> .delete(). In yet others it could depend on if a range, rather than
> >>>> a key, was used, or if the objectStore has indexes which might need
> updating.
> >>>>
> >>>> Ultimately I don't have a strong preference either way, though it
> >>>> seems unfortunate to slow down implementations for what likely is a
> rare use case.
> >>>>
> >>>> Let me know what you think.
> >>>>
> >>>> / Jonas
> >>>>
> >
> >>>To clarify, removing the return value from the sync call would change its
> return signature to void.  In this case, >>successfully returning from the
> IDBObjectStore.delete call would mean that the information was successfully
> >>deleted, correct?  If the information was not successfully deleted, would we
> throw an exception?
> >>>
> >>>In the async case, we would keep the same return value of IDBRequest for
> IDBObjectStore.delete.  The only change is >>that the request.result would be
> null, correct?  If no information is deleted or if part of the keyRange data is
> deleted, >>should we throw an error event?  It seems reasonable to me.
> >
> >>When you write "If no information is deleted ... should we throw an error
> event?" do you mean (1) there was no >matching key so the delete was a no-
> op, or (2) there was a matching key but an internal error occurred preventing
> the >delete? I ask because the second clause, "if part of the keyRange data is
> deleted, should we throw an error event?" >doesn't make sense to me in
> interpretation (1) since I'd expect sparse ranges in many cases.
> >
> > I was originally referring to (1) and (2).  However, after discussing this with
> a couple of folks we believe that the better approach would be to:
> > * continue to return true or false in the result.  This will take care of (1) and
> the successful deletion of all records.
> > * publish an error event if (2).  What I meant by (2) is that if there was a
> successful set of matches that were able to be returned by the keyRange, we
> should guarantee the deletion of all the matches or none.
> >
> > However, (2) brings up a bigger issue.  We are basically saying that if we
> support deletion of keyRanges we are guaranteeing that the batch operation
> will all happen or none of it will happen.  This implies some type of inner-
> transaction associated only with the delete operation, which could also be
> rolledback as part of the outer-transaction.  Otherwise, you could potentially
> preventDefault on any record that failed to be deleted and have your database
> in some type of inconsistent state.  Was that the intent?
> 
> This is already the case. For example when a inserting a value into an object
> store the implementation might need to go update several indexes. Updating
> one of these indexes might result in the violation of a 'unique' constraint at
> which point all changes to all indexes as well as the change to the object store
> must be rolled back. However no other changes done as part of the
> transaction should be rolled back (unless the resulting "error" event isn't
> canceled).
> 
> This is required in step 7 of the "Steps for asynchronously executing a
> request" (though I now see that it's missing in the "Steps for synchronously
> executing a request").
> 
> dvcs.w3.org/hg/IndexedDB/raw-file/tip/Overview.html#steps-for-
> asynchronously-executing-a-request
> 
> In the firefox implementation we create a "mini transaction" for each
> database request and if any part of the request fail we just roll back the "mini
> transaction".

You are correct!  I forgot that we also do something similar.
So if we fail to remove any one record from the keyRange set, should we throw an InvalidStateError, UnknownError, other?

> 
> >>In the async case, interpretation (1) matches Chrome's current behavior:
> success w/ null result if something was >deleted, error if there was nothing to
> delete. But I was about to land a patch to match the spec: success w/
> true/false, >so this thread is timely.
> >
> > Our current implementation matches the spec, so we are okay keeping it the
> way it is in the spec.  In either case, we need to figure out what to do when
> the partial deletion of keyRange records takes place.
> 
> So you are not worried that this might make it impossible to do further
> optimizations in the future?
> 
> Ultimately I'm ok either way. I don't have enough database experience to
> judge if we might loose out on important performance optimizations in the
> future. And I definitely think it's the case that if we make it return null then
> we'll force some people to do a .count() and then
> .delete() which is almost always slower.
> 
> / Jonas
> 

We don't see this being a perf issue for our implementation.  While it could be an issue for some implementations, based on our experience we don't see this being a big perf hit.

Israel
Received on Thursday, 27 October 2011 16:34:10 GMT

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