it says this is done so that other read processes can still
access the DB/table in it's OLD state w/o any hiccups.
I do not understand
so how does the MSSQL DB work when we alter table add column* *
2006/10/22, Ow Mun Heng [EMAIL PROTECTED]:
On Fri, 2006-10-20 at 09:06 -0700, William R. Mussatto wrote:
On Thu, October 19, 2006 18:24, Ow Mun Heng said:
Just curious to know,
I tried to update a table with ~1.7 million rows (~1G in size) and the
update took close to 15-20 minutes before it says it's done.
Is this kind of speed expected?
I don't really understand how the alter table add column is done, but
when I look at the show processlist I see that it says the state is
copying into tmp table
Does the alter table mean that MySQL has to copy the Entire table,
row-by-row into a temporary table, and add in the additional column
(or
2)??
Basic process for any change which modifies the structure of the table
is
to create a temporary table with the new structure, copy the information
from the old table table to the new one (modifying as needed to match
the
new structure), drop the old table and rename the new table to the old
tables name. So the time might be realistic. It depends on the hardware
you are using and what else is going on on the system.
I'm just a bit curious as to why this happens. Looking at the manuals /
books etc, it says this is done so that other read processes can still
access the DB/table in it's OLD state w/o any hiccups.
I'm just not too sold on that idea given that, for eg: a MSSQL server,
adds a new column in just secs rather than minutes on MySQL.
But anyway, I do understand what is happening right now.
Thanks.
(So, if I were to want to add a column to a Table which has a couple of
million rows, It would take a _looong_ time.
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