Re: (ITS#8430) Improved handling for large number of databases

[juerg.bircher@gmail.com]

---------- Forwarded message ----------
From: Juerg Bircher <juerg.bircher@gmail.com>
Date: Sat, May 28, 2016 at 10:30 PM
Subject: Re: (ITS#8430) Improved handling for large number of databases
To: Hallvard Breien Furuseth <h.b.furuseth@usit.uio.no>


On Sat, May 28, 2016 at 3:41 AM, Hallvard Breien Furuseth
<h.b.furuseth@usit.uio.no> wrote:
> On 28/05/16 03:28, Hallvard Breien Furuseth wrote:
>>
>> On 27/05/16 23:39, juerg.bircher@gmail.com wrote:
>>>
>>> Maybe I am overseeing something as I do not know all the thoughts
>>> between the lines.
>>
>>
>> With ITS#8431 I can think of one thing:
>> (...blah...)
>
>
> Actually the main reason I worry about lazy init is simply that
> we've screwed up DBIs many times, so I prefer to go slowly.
> That's Howard's call though, not mine.

Maybe a good way in between could be to memcpy
txn->mt_env->me_dbflags. However md_flags would need to be moved out
of the MDB_dbi struct like mt_dbflags or easier just add another array
serving as snapshot. This would not break anything with flag
initialization as we get a snapshot of them in the mdb_txn_renew0.
memcpy uses SSE instructions for x86_64. We should consider to align
on 16 byte boundary for best performance.
The dbflags could then still be initialized with MDB_UNSUSED as suggested.