From: Claudio Nanni
Date: May 7 2012 9:49am
Subject: =?GB2312?Q?Re=3A_=BB=D8=B8=B4=A3=BA_=BB=D8=B8=B4=A3=BA_Why_is_creating_indexes_fast?=
	=?GB2312?Q?er_after_inserting_massive_data_rows=3F?=
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too nice not to share it!

http://www.youtube.com/watch?v=3DINHF_5RIxTE



2012/5/7 Zhangzhigang <zzgang_2008@stripped>

> Thanks, i thought about this answer in the past, and i appreciate your
> reply.
>
>
>
> ________________________________
>  =B7=A2=BC=FE=C8=CB=A3=BA Alex Schaft <alexs@stripped>
> =CA=D5=BC=FE=C8=CB=A3=BA mysql@stripped
> =B7=A2=CB=CD=C8=D5=C6=DA=A3=BA 2012=C4=EA5=D4=C27=C8=D5, =D0=C7=C6=DA=D2=
=BB, =CF=C2=CE=E7 4:59
> =D6=F7=CC=E2: Re: =BB=D8=B8=B4=A3=BA Why is creating indexes faster after=
 inserting massive data
> rows?
>
> On 2012/05/07 10:53, Zhangzhigang wrote:
> > johan ....
> >> Plain and simple: the indices get updated after every insert statement=
,
> > whereas if you only create the index *after* the inserts, the index get=
s
> created in a single operation, which is a lot more efficient..
> >
> >
> > Ok, Creating the index *after* the inserts, the index gets created in a
> single operation.
> > But the indexes has to be updating row by row after the data rows has
> all been inserted. Does it work in this way?
> > So i can not find the different overhead  about two ways.
> My simplified 2c. When inserting rows with active indexes one by one
> (insert), mysql has to
>
> 1) lock the space for the data to be added,
> 2) write the data,
> 3) lock the index,
> 4) write the index key(s),
> 5) unlock the index,
> 6)unlock the data
>
> This happens for each row
>
> When first doing all data without index, only 1, 2, and 6 happen. When yo=
u
> then create an index, it can lock the index, read all the data and write
> all index keys in one go and then unlock the index.
>
> If you make an omelet, do you fetch your eggs from the fridge one by one,
> or all at the same time? :)
>
> HTH,
> Alex
>
>
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--=20
Claudio

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