Re: "Priority Mechanisms for OLTP and Transactional Web Applications"

Started by Dann Corbitover 20 years ago1 messages

DCorbit@connx.com

over 20 years ago

-----Original Message-----
From: cache+@cs.cmu.edu [mailto:cache+@cs.cmu.edu]
Sent: Monday, May 09, 2005 5:36 PM
To: Dann Corbit
Subject: RE: "Priority Mechanisms for OLTP and Transactional Web
Applications"

So how should we move forward on this? Do you have an application in
mind for this? Do you have any ideas on how the administrative
mechanism should be designed (prioritiziation based on client names,
user-based prioritization), etc?

I suspect that you have more experience in your modeling of the system
than I have. Probably, your ideas would be as good as or better than
those I might think of. I expect the PostgreSQL core team probably can
help you out more than I can as far as good ideas are concerned.

For the core team, see this paper for background:
http://www.db.cs.cmu.edu/Pubs/Lib/icde04oltp/oltp_icde04.pdf

My first inclination is that the postmaster should have a setting for
thread priority which would be nice to tune a particular machine for
maximum performance as a database server.

It would also be good to enable specific threads to get elevated
priority (perhaps a pqlib call or a modification to the query something
like {threadprio=<value>}

-david

Dann Corbit writes:

Yes. Something simple that can provide clear, tangible benefits is

the

best kind of improvement.

I am sure that adding parameters to the command line of PostgreSQL

which

enables superior tuning for differing computer systems would be

wildly

appreciated.

-----Original Message-----
From: cache+@cs.cmu.edu [mailto:cache+@cs.cmu.edu]
Sent: Wednesday, May 04, 2005 11:40 AM
To: Dann Corbit
Cc: harchol@cs.cmu.edu; natassa@cmu.edu; bianca@cs.cmu.edu;
cache@cs.cmu.edu
Subject: "Priority Mechanisms for OLTP and Transactional Web

Applications"

In our experimentation, we simply used a user-defined function to
handle changing the priority of transactions' threads. It

shouldn't

be hard to port the implementation back into postgres --- and
provide an administrative mechanism to assign priorities. Do you
think that PostgreSQL core would be interested in integrating
priorities of service in this manner? I'd be very interested in
helping out with this.

-David

Dann Corbit writes:

I have a question about your conclusion and the experiments as

they

relate to the PostgreSQL database. In the paper, we find

this:

"For example, we find that for PostgreSQL running under TPC-C,

the

simplest CPU scheduling algorithm CPU-Prio provides a factor

of 2

improvement for the high-priority transactions, and adding

priority

inheritance (CPU-Prio-Inherit) brings this up to a factor of

near

6

improvement under high loads, while hardly penalizing

low-priority

transactions. For PostgreSQL running under the TPC-W

workload, we

find

that the best scheduling algorithm is the simplest CPU

scheduling

policy

CPU-Prio, which improves performance for high-priority

transactions

by

a

factor of up to 5. The reason why inheritance is more

effective

for

the

TPC-C example above is that TPC-C has much more data

contention

than

TPC-W, leading to more priority inversions."

To change the scheduling of the threads, did you modify the

source

code

of the PostgreSQL database? If so, are the modifications

available?

It seems that you have achieved a very significant performance

boost by

a priority change, and I would be interested to know if the
modifications are available and also if they can be plowed

back

into

the

PostgreSQL core.

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I have a question about your conclusion and

the

experiments

as they relate to the PostgreSQL database.  In the paper,

find

this:<o:p></o:p>

<o:p> </o:p>

"For example, we find that for

PostgreSQL

running under

TPC-C, the simplest CPU scheduling algorithm CPU-Prio provides

factor

of 2

improvement for the high-priority transactions, and adding

priority

inheritance

(CPU-Prio-Inherit) brings this up to a factor of near 6

improvement

under high

loads, while hardly penalizing low-priority

transactions. 

For

PostgreSQL

running under the TPC-W workload, we find that the best

scheduling

algorithm is

the simplest CPU scheduling policy CPU-Prio, which improves

performance

for

high-priority transactions by a factor of up to 5. The reason

why

inheritance

is more effective for the TPC-C example above is that TPC-C

has

much

more data

contention than TPC-W, leading to more priority

inversions."<o:p></o:p>

<o:p> </o:p>

To change the scheduling of the threads,

did

you

modify the

source code of the PostgreSQL database?  If so, are the

modifications

available?<o:p></o:p>

<o:p> </o:p>

It seems that you have achieved a very

significant

performance boost by a priority change, and I would be

interested

to

know if

the modifications are available and also if they can be plowed

back

into the

PostgreSQL core.<o:p></o:p>

<o:p> </o:p>

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