On Tue, Apr 26, 2016 at 10:03 AM, Artem Tomyuk wrote:
> Hi All.
>
> I've noticed that there is a huge (more than ~3x slower) performance
> difference between KVM guest and host machine.
>
>
Is this unique to KVM, or do similar things happen with other virtualizers?
--
Mike Nolan
xes for that record, even if the index keys are not
changing. That's because any pending transactions still need to be able to
find the 'old' data, while new transactions need to be able to find the
'new' data. And ACID also means an update is essentially a
delete-and-insert.
--
Mike Nolan
r that an
update involves more work than an insert. Measuring that impact on
performance is probably a bit more challenging, because it's going to be
dependent on the specific table and the contents of the row, among other
things.
--
Mike Nolan
no...@tssi.com
nevertheless
> enforce the correct ordering of persisting fsync'd data? If you write to
> file A and fsync it, then write to another file B and fsync it too, is it
> guaranteed that if B is persisted, A is as well? Because if it isn't, you
> can end up with filesystem (or database) corruption anyway.
>
> - Heikki
>
>
The sad fact is that MANY drives (ssd as well as spinning) lie about their
fsync status.
--
Mike Nolan
On Fri, Jun 12, 2015 at 4:52 PM, David G. Johnston <
david.g.johns...@gmail.com> wrote:
> On Fri, Jun 12, 2015 at 4:37 PM, Michael Nolan wrote:
>
>> The only thing I can come up that's happened since last night was that we
>> ran the nightly vacuum analyze on that d
atistics target.
The parameters I was working with were:
effective_cache_size
shared_buffers
temp_buffers
work_mem
maintenance_work_mem
Looking at the free command, I see a lot more memory being used for
buffer/cache today. (Centos 7.)
--
Mike Nolan
no...@tssi.com
be from
3.13.X which as I understand it is a later kernel. Can you clarify which
3.X kernels are good to use and which are not?
--
Mike Nolan
isplay full headers for one
of the list messages to get the instructions from there.
--
Nolan Cafferky
Software Developer
IT Department
RBS Interactive
[EMAIL PROTECTED]
ed)
OR (f.PropertyId = g.PropertyId AND f.p_Modified_Date =
g.p_LastModified))
-- Luckys
--
Nolan Cafferky
Software Developer
IT Department
RBS Interactive
[EMAIL PROTECTED]
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TIP 1: if posting/reading th
Tom Lane wrote:
Nolan Cafferky <[EMAIL PROTECTED]> writes:
But, I'm guessing that random_page_cost = 1 is not a realistic value.
Well, that depends. If all your data can be expected to fit in memory
then it is a realistic value. (If not, you should be real car
Tom Lane wrote:
The first-order knob for tuning indexscan vs seqscan costing is
random_page_cost. What have you got that set to?
This is currently at the default of 4. All of my other planner cost
constants are at default values as well. Dropping it to 1 drops the
estimated cost by a compa
Questions:
* What can I do to reduce the estimated row count on the query?
* Why does clustering drive down the estimated cost for the index scan
so much? Does a change in correlation from .72 to 1 make that much of
a difference?
* Can I convince my query planner to index scan without clustering
I'm running postgres 8.0.7, and I've got a table of orders with about
100,000 entries. I want to just look at the new orders, right now 104 of
them.
EXPLAIN ANALYZE
SELECT
order_id
FROM
orders
WHERE
order_statuses_id = (SELECT id FROM order_statuses WHERE id_name
= 'new'
> This can often be called for. I'm working on a 400GB data warehouse right
> now, and almost *all* of our queries run from materialized aggregate tables.
I thought that was pretty much the definition of data warehousing! :-)
--
Mike Nolan
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, which is about 4200 transactions/second.
--
Mike Nolan
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tement instead of COPY.
The hardware is a Dell dual Xeon system, the disks are mirrored SATA
drives with write buffering turned off.
--
Mike Nolan
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TIP 4: Don't 'kill -9' the postmaster
at match the structure of
the tables they are logging.
2. Write a trigger function that converts columns to something you can
store in a common log table. (I've not found a way to do this without
inserting one row for each column being logged, though.)
--
Mike Nolan
---
le-clicks even
when they only want one click.
--
Mike Nolan
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TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
production server.
The same query a while later might respond quickly again.
I'm not sure where to look for the delay, either, and it is intermittent
enough that I'm not even sure what monitoring techniques to use.
--
Mike Nolan
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ammers working
on tuning issues for SQL Server than PostgreSQL has working on the
whole project.
--
Mike Nolan
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> Mike Nolan wrote:
> > Is there a way to copy a table INCLUDING the check constraints? If not,
> > then that information is lost, unlike varchar(n).
>
> "pg_dump -t" should work fine, unless I'm misunderstanding you.
I was specifically referring to doing
ar(n).
--
Mike Nolan
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rk as specified, I don't think
the standard cares much about what's happening behind the curtain.
--
Mike Nolan
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> Frankly, the only reason to use anything other than TEXT is compatibility with
> other databases and applications.
You don't consider a requirement that a field be no longer than a
certain length a reason not to use TEXT?
--
Mike Nolan
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when you've done your homework".
Can they call you at the unemployment office?
--
Mike Nolan
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build indexes on a regular basis,
even if you move that field into a separate table.
--
Mike Nolan
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TIP 7: don't forget to increase your free space map settings
ery with a 'where in' clause that couldn't be written
as a join. I think linguistically 'where in' may even be a special
case of 'join'.
Yet another question for the theoretists: Would it be possible to optimize
a 'where in' query by rewriting it as
> select * from attributes_table where id in (select id from
> attributes where (name='obsid') and (value='oid00066'));
Can you convert it into a join? 'where in' clauses tend to slow pgsql
down.
--
Mike Nolan
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