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From Denis Magda <dma...@gridgain.com>
Subject Re: Possible optimizations for SQL + Off-heap
Date Thu, 21 Apr 2016 19:59:07 GMT
Sergi,

However if we implement non snapshotable data structure to hold indexes (skip list or b-tree)
then it will be feasible to optimize point 1) - working with off-heap data with BinaryObjectOffHeapImpl.
Am I right?

—
Denis

> On Apr 21, 2016, at 5:27 PM, Sergi Vladykin <sergi.vladykin@gmail.com> wrote:
> 
> 1. In general it is not possible to keep BinaryObject in "attached" state, because at
the query end we release snapshots and the entry can be concurrently removed with offheap
memory deallocation, while result row is still needed.
> 
> 2. Of course there are multiple alternatives (skiplist or b+tree), but we'll need to
implement them over offheap memory, this will take some time...
> 
> Sergi
>  
> 
> Sergi
> 
> 2016-04-21 16:48 GMT+03:00 Denis Magda <dmagda@gridgain.com <mailto:dmagda@gridgain.com>>:
> Sergi, Igniters,
> 
> Big deployments store enormous amount of data in off-heap. If to keep using such deployments
under high load executing SQL queries and basic cache operations in parallel then it’s easy
to see that Java heap pressure grows due to the bigger number of short live objects creation.
> 
> I’ve been investigating Ignite code and noted the following
> 
> 1) During SQL query execution off-heap data is unswapped and stored in BinaryObjectImpl
wrapper for columns comparison. Also as I see the same happens when an index is updated.
> 
> 2) Off-heap index tree is snapshotable. Taking into account hight update and query rates,
Java heap will be populated with much more short snapshots.
> 
> Actually I think that we can try to lower the impact caused by 1) by trying reusing BinaryObjectOffHeapImpl
that allows to access fields directly working with off-heap. What do you think, any obstacles?
> 
> In regards to the second. Is there any alternatives to snapshotable tree in general?
> 
> —
> Denis
> 


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