回复： 回复： Why is creating indexes f aster after inserting massive data rows?

[Zhangzhigang]

Ok, but my opinion is that the sorting algorithms is not impact this difference, two
ways  all do B+ tree inserts.


________________________________
 发件人： Claudio Nanni <claudio.nanni@stripped>
收件人： Zhangzhigang <zzgang_2008@stripped> 
抄送： Johan De Meersman <vegivamp@stripped>; "mysql@stripped"
<mysql@stripped> 
发送日期： 2012年5月7日, 星期一, 下午 5:01
主题: Re: 回复： Why is creating indexes faster after inserting massive data rows?
 

Creating the index in one time is one macro-sort operation,
updating the index at every row is doing the operation on and on again.
If you do not understand the difference I recommend you to read some basics about sorting
algorithms,
very interesting read anyway.

Claudio 


2012/5/7 Zhangzhigang <zzgang_2008@stripped>

johan ....
>
>>Plain and simple: the indices get updated after every insert statement,
>whereas if you only create the index *after* the inserts, the index gets 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.
>
>
>
>
>
>________________________________
> 发件人： Johan De Meersman <vegivamp@stripped>
>
>收件人： Zhangzhigang <zzgang_2008@stripped>
>抄送： mysql@stripped
>发送日期： 2012年5月7日, 星期一, 下午 4:28
>
>主题: Re: Why is creating indexes faster after inserting massive data rows?
>
>
>----- Original Message -----
>> From: "Zhangzhigang" <zzgang_2008@stripped>
>>
>> Creating indexes after inserting massive data rows is faster than
>> before inserting data rows.
>> Please tell me why.
>
>Plain and simple: the indices get updated after every insert statement, whereas if
you only create the index *after* the inserts, the index gets created in a single
operation, which is a lot more efficient.
>
>I seem to recall that inside of a transaction (thus, InnoDB or so) the difference is
markedly less; I might be wrong, though.
>
>
>--
>Bier met grenadyn
>Is als mosterd by den wyn
>Sy die't drinkt, is eene kwezel
>Hy die't drinkt, is ras een ezel


-- 
Claudio