subject:"\[appengine\-java\] no async queries on AsyncDatastoreService for 1.4.0\?"

Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

2010-12-07 Thread Maxim Veksler

Hi Max,

Could you please provide input on the following design:

We design for DataSource redundancy. For this we've built a flow which
obtains data from 2 sources: First from GAE DataSource using PreparedQuery
and if that fails (0.5sec timeout) from our backup service feed which we
access using URLFetch (auto scaled EC2 nodes).

We strive for maximum performance, So we plan to issue async call to each of
the data sources and later when the data becomes required poll the 2
sources, using the first one available.

As for the URLFetch service, we will use this patten:
FutureHTTPResponse f = fetchService.fetchAsync(request);
...
if(f.isDone()) { ... }

But for PreparedQuery.asIterator(), I'm not sure how this is implement on
your side. I would love an answer confirming that this code will not block
on hasNext() (While datasource is asynchronously getting results)?

IteratorEntity iterator =
getAsyncDatastoreService().prepare(findGeoIP).asIterator();

if(iterator.hasNext()) { ... }

Thanks for the insights.

Maxim.

On Mon, Nov 29, 2010 at 9:08 PM, Max Ross (Google)
maxr+appeng...@google.com maxr%2bappeng...@google.com wrote:

Hi Luke,

First the awesome news:
As of 1.4.0, many queries are implicitly asynchronous. When you call
PreparedQuery.asIterable() or PreparedQuery.asIterator(), we initiate the
query in the background and then immediately return. This lets you do work
while the first batch of results is being fetched. And, when the first
batch has been consumed we immediately request the next batch. If you're
performing a significant amount of work with each Entity as you iterate you
will probably see a latency win as a result of this.

Now the less awesome news:
We didn't get around to making the List returned by PreparedQuery.asList()
work this same magic, but you can expect this in a future release.

Some deeper thoughts:
The underlying RPCs between your app and the datastore fetch results in
batches. We fetch an initial batch of results, and once that batch has been
consumed we fetch the next batch. But, there's nothing in the API that maps
to these batches - it's either a List containing the entire result set or an
Iterable/Iterator that returns Entities one at a time. An API that provides
async access to the individual results returned by an Iterable/Iterator
(IteratorFutureEntity) doesn't really make sense since you don't know
which call to hasNext() is going to require a new batch to be fetched, and
without that knowledge, the knowledge of what is going to trigger something
expensive, you can't really make appropriate use of an asynchronous API.

Going forward, we're definitely interested in exposing these batches
directly, and an explicitly async API for these batches makes a lot of sense
since fetching these batches would map directly to something expensive on
the server side.

Hope this helps,
Max

On Fri, Nov 26, 2010 at 4:41 PM, Luke lvale...@gmail.com wrote:

i was taking a look at the 1.4.0 javadoc for AsyncDatastoreService. i
see the get, put and delete operations return a Future, but the
prepare methods return a naked PreparedQuery object, and it doesn't
look like PreparedQuery has any async get methods.

does the AsyncDatastoreService not support asynchronous queries, or is
there something i'm missing?

glad to see at lets the get and put methods are async, hoping to get
async queries too (as well as async interfaces to more services).

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Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

2010-12-07 Thread Alfred Fuller

Currently hasNext() will block on the first batch of results. There is
currently no way to do what you are asking in Java.

On Tue, Dec 7, 2010 at 2:40 AM, Maxim Veksler ma...@vekslers.org wrote:

Hi Max,

Could you please provide input on the following design:

We strive for maximum performance, So we plan to issue async call to each
of the data sources and later when the data becomes required poll the 2
sources, using the first one available.

As for the URLFetch service, we will use this patten:
FutureHTTPResponse f = fetchService.fetchAsync(request);
...
if(f.isDone()) { ... }

IteratorEntity iterator =
getAsyncDatastoreService().prepare(findGeoIP).asIterator();

if(iterator.hasNext()) { ... }

Thanks for the insights.

Maxim.

On Mon, Nov 29, 2010 at 9:08 PM, Max Ross (Google)
maxr+appeng...@google.com maxr%2bappeng...@google.com wrote:

Hi Luke,

Now the less awesome news:
We didn't get around to making the List returned by PreparedQuery.asList()
work this same magic, but you can expect this in a future release.

Hope this helps,
Max

On Fri, Nov 26, 2010 at 4:41 PM, Luke lvale...@gmail.com wrote:

does the AsyncDatastoreService not support asynchronous queries, or is
there something i'm missing?

glad to see at lets the get and put methods are async, hoping to get
async queries too (as well as async interfaces to more services).

Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

2010-12-07 Thread Maxim Veksler

Thank you for the information.

We kinda expected that the current implementation will block...
In case anyone wonders our current worked out design is as following: Do
async get to EC2 (takes ~270ms) and right after that do blocking get to
datastore (with timeout of 300ms).

Because we know URLFetch to ec2 takes ~270ms and is async we get to enjoy
both worlds even with a blocking DataStore:

Option A: Datastore has no problems, meaning that it will reply to
PreparedQuery with 15ms. In this case we don't bother with the async call we
just did and just continue normal flow.
Option B: Datastore has problems, and will block. In this case the 300ms
query will time out, after which we will attempt to access the Future.get()
of URLFetch where we expect to have a result.

So... If today we did (at maximum) 500ms datastore get + 270ms URLFetch get
= total of 770ms just for the query after I get implemented we should be
doing (at maximum) query in 300ms.

Kinda of cool.


Maxim.

On Tue, Dec 7, 2010 at 3:39 PM, Alfred Fuller
arfuller+appeng...@google.comarfuller%2bappeng...@google.com
 wrote:

 Currently hasNext() will block on the first batch of results. There is
 currently no way to do what you are asking in Java.

 On Tue, Dec 7, 2010 at 2:40 AM, Maxim Veksler ma...@vekslers.org wrote:

 Hi Max,

 Could you please provide input on the following design:

 We design for DataSource redundancy. For this we've built a flow which
 obtains data from 2 sources: First from GAE DataSource using PreparedQuery
 and if that fails (0.5sec timeout) from our backup service feed which we
 access using URLFetch (auto scaled EC2 nodes).

 We strive for maximum performance, So we plan to issue async call to each
 of the data sources and later when the data becomes required poll the 2
 sources, using the first one available.

  As for the URLFetch service, we will use this patten:
 FutureHTTPResponse f = fetchService.fetchAsync(request);
 ...
 if(f.isDone()) { ... }

 But for PreparedQuery.asIterator(), I'm not sure how this is implement on
 your side. I would love an answer confirming that this code will not block
 on hasNext() (While datasource is asynchronously getting results)?

 IteratorEntity iterator =
 getAsyncDatastoreService().prepare(findGeoIP).asIterator();
 
 if(iterator.hasNext()) { ... }



  Thanks for the insights.

 Maxim.

 On Mon, Nov 29, 2010 at 9:08 PM, Max Ross (Google) 
 maxr+appeng...@google.com maxr%2bappeng...@google.com wrote:

 Hi Luke,

 First the awesome news:
 As of 1.4.0, many queries are implicitly asynchronous.  When you call
 PreparedQuery.asIterable() or PreparedQuery.asIterator(), we initiate the
 query in the background and then immediately return.  This lets you do work
 while the first batch of results is being fetched.  And, when the first
 batch has been consumed we immediately request the next batch.  If you're
 performing a significant amount of work with each Entity as you iterate you
 will probably see a latency win as a result of this.

 Now the less awesome news:
 We didn't get around to making the List returned by
 PreparedQuery.asList() work this same magic, but you can expect this in a
 future release.

 Some deeper thoughts:
 The underlying RPCs between your app and the datastore fetch results in
 batches.  We fetch an initial batch of results, and once that batch has been
 consumed we fetch the next batch.  But, there's nothing in the API that maps
 to these batches - it's either a List containing the entire result set or an
 Iterable/Iterator that returns Entities one at a time.  An API that provides
 async access to the individual results returned by an Iterable/Iterator
 (IteratorFutureEntity) doesn't really make sense since you don't know
 which call to hasNext() is going to require a new batch to be fetched, and
 without that knowledge, the knowledge of what is going to trigger something
 expensive, you can't really make appropriate use of an asynchronous API.

 Going forward, we're definitely interested in exposing these batches
 directly, and an explicitly async API for these batches makes a lot of sense
 since fetching these batches would map directly to something expensive on
 the server side.

 Hope this helps,
 Max

 On Fri, Nov 26, 2010 at 4:41 PM, Luke lvale...@gmail.com wrote:

 i was taking a look at the 1.4.0 javadoc for AsyncDatastoreService.  i
 see the get, put and delete operations return a Future, but the
 prepare methods return a naked PreparedQuery object, and it doesn't
 look like PreparedQuery has any async get methods.

 does the AsyncDatastoreService not support asynchronous queries, or is
 there something i'm missing?

 glad to see at lets the get and put methods are async, hoping to get
 async queries too (as well as async interfaces to more services).

 --
 You received this message because you are subscribed to the Google
 Groups Google App Engine for Java group.
 To post to this group, send email to
 google-appengine-j...@googlegroups.com.
 To

[appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

2010-11-29 Thread Luke

i was taking a look at the 1.4.0 javadoc for AsyncDatastoreService.  i
see the get, put and delete operations return a Future, but the
prepare methods return a naked PreparedQuery object, and it doesn't
look like PreparedQuery has any async get methods.

does the AsyncDatastoreService not support asynchronous queries, or is
there something i'm missing?

glad to see at lets the get and put methods are async, hoping to get
async queries too (as well as async interfaces to more services).

-- 
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Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

2010-11-29 Thread Max Ross (Google)

Hi Luke,

Now the less awesome news:
We didn't get around to making the List returned by PreparedQuery.asList()
work this same magic, but you can expect this in a future release.

Hope this helps,
Max

On Fri, Nov 26, 2010 at 4:41 PM, Luke lvale...@gmail.com wrote:

does the AsyncDatastoreService not support asynchronous queries, or is
there something i'm missing?

glad to see at lets the get and put methods are async, hoping to get
async queries too (as well as async interfaces to more services).

--
You received this message because you are subscribed to the Google Groups
Google App Engine for Java group.
To post to this group, send email to google-appengine-j...@googlegroups.com.
To unsubscribe from this group, send email to
google-appengine-java+unsubscr...@googlegroups.com.
For more options, visit this group at
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Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

[appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

Re: [appengine-java] no async queries on AsyncDatastoreService for 1.4.0?

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