Re: Async queries

[Charulata Sharma (charshar)]

Thanks Andy for the detailed explanation. I have added the callback feature and 
am going to test if this helps.

Charu

From: Andy Tolbert <andrew.tolb...@datastax.com>
Reply-To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Date: Monday, October 2, 2017 at 5:48 PM
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Subject: Re: Async queries

Hi Charu,

Since the driver uses Guava futures, you can use some of the methods in 
Futures<https://google.github.io/guava/releases/19.0/api/docs/com/google/common/util/concurrent/Futures.html>
 to add listeners, callbacks and transformers that are invoked when the future 
completes without blocking the calling thread like getUninterruptibly does.  
For example, the following registers a callback whose onSuccess or onFailure 
method is called based on the success of the query.

Futures.addCallback(future, new FutureCallback() {
public void onSuccess(ResultSet result) {
// process result
}

public void onFailure(Throwable t) {
// log exception
}
});

You can read more about using the driver's async features 
here<http://docs.datastax.com/en/developer/java-driver/3.3/manual/async/>.

Since executeAsync does not block, you'll want to be careful of is not 
submitting too many requests at a time as this can degrade performance and may 
explain what you are observing.  One simple (although somewhat crude) way of 
handling this is to use a Semaphore with a fixed number of permits.  You would 
acquire a Semaphore permit before you execute a query, and then release a 
permit in a callback on completion of the request.  This would cause your 
calling thread to block whenever you run out of permits, and then continue when 
a query completes and releases a permit.

The upcoming version (4.0) of the java driver uses 
CompletionStage/CompletableFuture (java 8 futures), although we'll probably 
provide a guava extension as well for those who still want to use 
ListenableFuture.

Thanks,
Andy


On Mon, Oct 2, 2017 at 6:44 PM Charulata Sharma (charshar) 
<chars...@cisco.com<mailto:chars...@cisco.com>> wrote:
Hi ,


We are observing some performance issues when executing a large number of 
read/write queries.
We use executeAsync query for most of our read and write requests and then 
future.getUninterruptibly() methods before returning to the client application.


Code snippet is:  (In the bind portion we have some GSON object conversions.

 List futures = new ArrayList<>();

  BoundStatement bind ;
  For(loop condition) {
bind =PreparedStatement.bind(….) //The PreparedStatement is prepared 
outside the loop.
   resultSetFuture = SESSION.executeAsync(bind);
 futures.add(resultSetFu ture);
  }

for(ResultSetFuture future: futures){
   future.getUninterruptibly();
}


Reading through the documents , I found that although the queries are executed 
in an async fashion, the future. getUninterruptibly(), is a blocking call.
I am trying to implement a callable future, but wanted to know from the 
community if there is any better way of doing this and if changing to callable 
future will help.


Thanks,
Charu

Re: Async queries

[Andy Tolbert]

Hi Charu,

Since the driver uses Guava futures, you can use some of the methods in
Futures

to
add listeners, callbacks and transformers that are invoked when the future
completes without blocking the calling thread like getUninterruptibly
does.  For example, the following registers a callback whose onSuccess or
onFailure method is called based on the success of the query.

Futures.addCallback(future, new FutureCallback() {
public void onSuccess(ResultSet result) {
// process result
}

public void onFailure(Throwable t) {
// log exception
}
});

You can read more about using the driver's async features here
.

Since executeAsync does not block, you'll want to be careful of is not
submitting too many requests at a time as this can degrade performance and
may explain what you are observing.  One simple (although somewhat crude)
way of handling this is to use a Semaphore with a fixed number of permits.
You would acquire a Semaphore permit before you execute a query, and then
release a permit in a callback on completion of the request.  This would
cause your calling thread to block whenever you run out of permits, and
then continue when a query completes and releases a permit.

The upcoming version (4.0) of the java driver uses
CompletionStage/CompletableFuture (java 8 futures), although we'll probably
provide a guava extension as well for those who still want to use
ListenableFuture.

Thanks,
Andy


On Mon, Oct 2, 2017 at 6:44 PM Charulata Sharma (charshar) <
chars...@cisco.com> wrote:

> Hi ,
>
>
>
>
>
> We are observing some performance issues when executing a large number of
> read/write queries.
>
> We use executeAsync query for most of our read and write requests and then
> future.getUninterruptibly() methods before returning to the client
> application.
>
>
>
>
>
> Code snippet is:  (In the bind portion we have some GSON object
> conversions.
>
>
>
>  List futures = *new* ArrayList<>();
>
>
>
>   BoundStatement bind ;
>
>   For(loop condition) {
>
> bind =PreparedStatement.bind(….) //The PreparedStatement is
> prepared outside the loop.
>
>resultSetFuture = *SESSION*.executeAsync(bind);
>
>
>  futures.add(resultSetFu ture);
>
>   }
>
>
>
> *for*(ResultSetFuture future: futures){
>
>future.getUninterruptibly();
>
> }
>
>
>
>
>
> Reading through the documents , I found that although the queries are
> executed in an async fashion, the future. getUninterruptibly(), is a
> blocking call.
>
> I am trying to implement a callable future, but wanted to know from the
> community if there is any better way of doing this and if changing to
> callable future will help.
>
>
>
>
>
> Thanks,
>
> Charu
>

Async queries

[Charulata Sharma (charshar)]

Hi ,


We are observing some performance issues when executing a large number of 
read/write queries.
We use executeAsync query for most of our read and write requests and then 
future.getUninterruptibly() methods before returning to the client application.


Code snippet is:  (In the bind portion we have some GSON object conversions.

 List futures = new ArrayList<>();

  BoundStatement bind ;
  For(loop condition) {
bind =PreparedStatement.bind(….) //The PreparedStatement is prepared 
outside the loop.
   resultSetFuture = SESSION.executeAsync(bind);
 futures.add(resultSetFu ture);
  }

for(ResultSetFuture future: futures){
   future.getUninterruptibly();
}


Reading through the documents , I found that although the queries are executed 
in an async fashion, the future. getUninterruptibly(), is a blocking call.
I am trying to implement a callable future, but wanted to know from the 
community if there is any better way of doing this and if changing to callable 
future will help.


Thanks,
Charu