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Date: Mon, 10 Feb 2020 12:49:24 +0300
From: Konstantin Osipov <kostja.osipov@gmail.com>
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Subject: Re: [Tarantool-patches] [PATCH v3 2/2] memtx: allow quota overuse
 for truncation and deletion
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To: Ilya Kosarev <i.kosarev@tarantool.org>
Cc: tarantool-patches@dev.tarantool.org, v.shpilevoy@tarantool.org

* Ilya Kosarev <i.kosarev@tarantool.org> [20/02/10 11:26]:
> 
> As far as i see, memtx reserves extents using specific pool and
> mempool_alloc. We will need to implement additional feature to reserve
> slabs in memtx arena and provide them specifically for truncation
> needs.

Yes. But the way you say it sounds negative. Are you suggesting
not implementing this feature and just hacking in quota bypass is
better? Why?

> However, after that we will encounter the necessity to calculate
> how much space we need to reserve for truncation tuples.

No. 1 slab is enough.

> I guess we
> might want to reserve a truncation buf for each created space and
> re-reserve it on each truncation, although such logic seems
> overcomplicated.

Indeed, this would be strange.

> Furthermore, the problem with space:delete() might happen exactly when
> we are trying to reserve a slab to guarantee successful statement-level
> rollback. This can't be fixed using reservation tech. 

Two events can't happen at the same time in a single-threaded
application. Please take time to explain what you mean here. 


-- 
Konstantin Osipov, Moscow, Russia