On Mon, Oct 26, 2015 at 9:03 AM, Любен Каравелов <karavelov@mail.bg> wrote: > > > ----- Цитат от Kisung Kim (kskim@bitnine.co.kr), на 26.10.2015 в 04:36 ----- > > > However, what I want to know is about the update performance difference > > between PG and Oracle if there any. > > The case I described is for exaggerating the difference between PG and > > Oracle. > > > > I want to explain for our clients that PG's update performance is > > comparable to Oracle's. > > > > Oracle is also using MVCC but copies the old row in the rollback segment and > rewrites the values in-place.
I think Oracle just copies the changed part of old row to rollback segment.
Also in Redo logs, it just writes the changed column value (both old and
new). So for the case we are discussing in this thread (one changed
column out of 200 columns), Oracle will just write the old value of that
column in Redo and then in rollback segment, and write the new value
in Redo and then do the in-place update in heap row.
In that case, readers would pay the penalty for constructing the row. PostgreSQL will not incur the cost of reconstruction. Either writer or reader is bound to pay penalty. If the user's load is reader heavy it makes sense to use something like PG, else something like what is described above.
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Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company