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From Ravikumar Govindarajan <ravikumar.govindara...@gmail.com>
Subject Re: SlabAllocationCacheValueBufferPool thread-safe?
Date Wed, 10 Aug 2016 14:37:18 GMT
Aaron,

Just one more help...

I hardcoded _quiet=true in CacheIndexInput.java and started the
shard-server. It seems to mangle the cached-bytes & results in IOException
during searches. Merges however work smoothly...

I do know that _quiet is meant only for merge. But there is a use-case I am
working on, which will need this setting during searches also...

Any quick suggestions for this issue?

--
Ravi

On Thu, Aug 4, 2016 at 2:43 PM, Aaron McCurry <amccurry@gmail.com> wrote:

> Ok. Thanks!  I will patch the code and run some tests.
>
> On Monday, August 1, 2016, Ravikumar Govindarajan <
> ravikumar.govindarajan@gmail.com> wrote:
>
> > We did a simple expiry check. Works fine as of now...
> >
> > private CacheValue lookup(boolean quietly) {
> >
> >     CacheValue cacheValue = _indexInputCache.get(_key.getBlockId());
> >
> >     if(cacheValue == null || *cacheValue.isExpired()*) {
> >
> >      ....
> >
> >     }
> >
> > }
> >
> > On Sun, Jul 31, 2016 at 2:14 AM, Aaron McCurry <amccurry@gmail.com
> > <javascript:;>> wrote:
> >
> > > Ok I have to look into it.  Do you have a patch available?
> > >
> > > On Thu, Jul 28, 2016 at 4:47 AM, Ravikumar Govindarajan <
> > > ravikumar.govindarajan@gmail.com <javascript:;>> wrote:
> > >
> > > > One issue we found in CacheIndexInput.java which is causing NPE
> > > >
> > > >   private CacheValue lookup(boolean quietly) {
> > > >
> > > >     CacheValue cacheValue = _indexInputCache.get(_key.getBlockId());
> > > >
> > > >      .......
> > > >
> > > >      return cacheValue;
> > > >
> > > >      //There is no eviction check for the CacheValue returned from
> > > > IndexInputCache, causing NPE
> > > >
> > > >   }
> > > >
> > > > Also, lookup method blindly adds to _indexInputCache before
> returning.
> > > > Instead, it would be better if it is done inside the null-check
> loop...
> > > >
> > > > On Fri, Jul 22, 2016 at 6:09 PM, Ravikumar Govindarajan <
> > > > ravikumar.govindarajan@gmail.com <javascript:;>> wrote:
> > > >
> > > > > Thanks for the feedback Aaron
> > > > >
> > > > > On Thu, Jul 21, 2016 at 6:42 PM, Aaron McCurry <amccurry@gmail.com
> > <javascript:;>>
> > > > wrote:
> > > > >
> > > > >> On Thu, Jul 21, 2016 at 1:55 AM, Ravikumar Govindarajan <
> > > > >> ravikumar.govindarajan@gmail.com <javascript:;>> wrote:
> > > > >>
> > > > >> > Just now saw BlockLocks code. It is documented to be
> thread-safe.
> > > > >> Apologize
> > > > >> > for the trouble...
> > > > >> >
> > > > >> > Btw, a small nit. The below method is not returning true.
Is
> that
> > > > >> > intentional?
> > > > >> >
> > > > >> >     boolean releaseIfValid(long address) {
> > > > >> >
> > > > >> >       if (address >= _address && address <
_maxAddress) {
> > > > >> >
> > > > >> >         long offset = address - _address;
> > > > >> >
> > > > >> >         int index = (int) (offset / _chunkSize);
> > > > >> >
> > > > >> >         _locks.clear(index);
> > > > >> >
> > > > >> >       }
> > > > >> >
> > > > >> >       return false;
> > > > >> >
> > > > >> >     }
> > > > >> >
> > > > >>
> > > > >> In my 30 second review I think you are right.  It should probably
> > > return
> > > > >> true.  However I want to alanyze what happens with the current
> code
> > > so I
> > > > >> can write a test that proves there is a problem (because there
> > > probably
> > > > >> is)
> > > > >> and fix it.
> > > > >>
> > > > >>
> > > > >> >
> > > > >> > Also, I thought a background thread can attempt merging
sparsely
> > > > >> populated
> > > > >> > slabs into one single slab & release free-mem (in 128MB
chunks)
> > back
> > > > to
> > > > >> > OS...
> > > > >> >
> > > > >>
> > > > >> I think this is a good idea, I just didn't get to writing it.
> > > > >>
> > > > >>
> > > > >> >
> > > > >> > You think it could be beneficial or it would make it needlessly
> > > > complex?
> > > > >> >
> > > > >>
> > > > >> I think for dedicated servers is might be overkill, but for a
> mixed
> > > > >> workload environment (think docker containers and the like) it
> would
> > > be
> > > > >> useful.
> > > > >>
> > > > >> Aaron
> > > > >>
> > > > >>
> > > > >> >
> > > > >> > On Wed, Jul 20, 2016 at 11:38 PM, Aaron McCurry <
> > amccurry@gmail.com <javascript:;>
> > > >
> > > > >> > wrote:
> > > > >> >
> > > > >> > > I don't think there is a race condition because the
allocation
> > > > occurs
> > > > >> > > atomically in the BlockLocks class.  Do see a problem?
 Let me
> > > know.
> > > > >> > >
> > > > >> > > Aaron
> > > > >> > >
> > > > >> > > On Wed, Jul 20, 2016 at 9:19 AM, Ravikumar Govindarajan
<
> > > > >> > > ravikumar.govindarajan@gmail.com <javascript:;>>
wrote:
> > > > >> > >
> > > > >> > > > I came across the following in
> > > > >> SlabAllocationCacheValueBufferPool.java.
> > > > >> > > Is
> > > > >> > > > the below method thread-safe?
> > > > >> > > >
> > > > >> > > >  @Override
> > > > >> > > >
> > > > >> > > >   public CacheValue getCacheValue(int cacheBlockSize)
{
> > > > >> > > >
> > > > >> > > >     validCacheBlockSize(cacheBlockSize);
> > > > >> > > >
> > > > >> > > >     int numberOfChunks = getNumberOfChunks(cacheBlockSize);
> > > > >> > > >
> > > > >> > > >     ...
> > > > >> > > >
> > > > >> > > >    }
> > > > >> > > >
> > > > >> > > >
> > > > >> > > > It does allocation in a tight-loop using BlockLocks,
Slab &
> > > > Chunks.
> > > > >> Is
> > > > >> > > > there a race-condition where 2 threads can pick
same slab &
> > > chunk?
> > > > >> > > >
> > > > >> > >
> > > > >> >
> > > > >>
> > > > >
> > > > >
> > > >
> > >
> >
>

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