Re: JournalDiskSyncStrategy?

My suggestion:

https://github.com/jsampson/prevayler/pull/9

On 11 Aug 2014, at 21:53, Justin Sampson <[email protected]> wrote:

> Karl Wettin wrote:
> 
>> What I do is to place a transient object graph of a given root
>> object on a queue which is polled by a single thread which
>> evaluate the delta which produce and execute transactions.
>> Sometimes as many as 200 transaction from a single delta. 
>> 
>> Usually I manage to empty this queue a every few seconds when
>> not syncing on each transaction. It would be nice to sync at
>> that point.
>> 
>> Running FS.sync on each and every transaction produced from the
>> delta of a transient root object graph takes up to 10 seconds
>> on my slow HDD, usually 5-7, while not syncing takes 1-3
>> milliseconds.
> 
> Oh, interesting. Prevayler tries to batch multiple transactions
> into a single disk sync, but the current implementation is
> thread-based: The number of transactions per batch is bounded by
> the number of threads that are submitting transactions. You
> probably don't want to create 200 threads just to submit those
> 200 transactions.
> 
> If the Prevayler interface were redesigned to be asynchronous,
> you could submit all 200 transactions without waiting for them to
> complete, and Prevayler could take care of batching them for you.
> Unfortunately that would require some nontrivial redesign of
> Prevayler's internals.
> 
> A less drastic change would be to add a single new method to the
> Prevayler interface, e.g.:
> 
> void executeAll(Iterable<? extends Transaction<? super P>>)
> 
> The implementation could then ensure that all of the given
> transactions get batched into a single disk sync.
> 
> For that matter, even without any changes to Prevayler, you could
> combine your 200 individual transactions into a single composite
> transaction with the same effect, e.g.:
> 
> public final class CompositeTransaction<P>
>    implements Transaction<P>, Serializable {
>  private final List<Transaction<P>> transactions;
>  public CompositeTransaction(
>      Collection<? extends Transaction<P>> transactions) {
>    this.transactions = new ArrayList<>(transactions);
>  }
>  public void executeOn(P prevalentSystem, Date executionTime) {
>    for (Transaction<P> transaction : transactions) {
>      transaction.executeOn(prevalentSystem, executionTime);
>    }
>  }
> }
> 
> Since you're not actually wanting to turn off disk sync, just
> make it more efficient, one of these options might be preferable
> to making the disk sync logic itself more configurable.
> 
> Cheers,
> Justin
> 
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