Bruce,
Let me answer to your question.
Question 1: How much faster is it ?
To answer to your question, I measured execution times of INSERT
operations on concurrent accesses on dual-core x 2 CPU (each 2.80GHz),
In the experiment, each client issues 5000 INSERT operations concurrently.
The following shows the average times (seconds) of 5 measurements.
#Cli: The number of concurrent clients
P-D: PostgreSQL Default (i.e. usual file system)
P-T: PostgreSQL tmpfs
S-D: Sigres Default (i.e. usual file system)
S-T: Sigres tmpfs
P-T/S-T Improve ratio of S-T to P-T
The result shows S-T is 10% to 18% faster than P-T.
Thus my answer to your question is 10% to 18% when concurrency is from1
to 100.
#Cli P-D P-T S-D S-T P-T/S-T
1 1.72 0.50 0.46 0.45 1.10
2 2.87 0.62 0.58 0.54 1.15
3 3.08 0.89 0.77 0.77 1.15
4 3.14 0.98 0.86 0.84 1.16
5 3.31 1.23 1.09 1.07 1.15
6 3.57 1.44 1.31 1.27 1.14
7 3.91 1.68 1.51 1.48 1.14
8 4.49 1.89 1.71 1.67 1.13
9 4.78 2.21 1.9 1.92 1.15
10 5.33 2.47 2.22 2.14 1.15
20 11.50 5.66 5.16 4.86 1.16
50 32.96 16.54 14.92 13.97 1.18
100 79.60 43.71 39.55 38.38 1.14
Question 2: Is that worth adding extra code to improve it ?
Yes, I think it is worth. It is because in the case of commercial DBMS,
only 5% improvement is achieved with version-up.
BTW, I and a friend of mine try to design & implement a parallel access
way to the wal buffer on a shared memory. I think this is promising
direction since WALInsertLock is more frequently issued than
WALWriteLock, and the number of CPU-cores will increase definitely.
-- Hideyuki
Bruce Momjian wrote:
Hideyuki Kawashima wrote:
Bruce,
Thanks for your comments, and let me answer to your question.
Sigres is *not* significantly faster than just creating a file system on
the permanent memory and putting xlog on there.
Sigres is slightly faster than the case because each backend does not
call XLogWrite while bgWriter does.
The question then is how much faster is it, and is that worth adding
extra code to improve it.
---------------------------------------------------------------------------
-- Hideyuki
Bruce Momjian wrote:
Tom Lane wrote:
Gene <[EMAIL PROTECTED]> writes:
... just my two cents. on a side note, would putting the wal on a
tmpfs partition give you something similar?
Indeed, I'm wondering why one needs to hack the Postgres core to throw
away data integrity guarantees; there are plenty of ways to do that
already :-(. Hideyuki-san has not explained exactly what integrity
assumptions he wants to make or not make. I'm surely willing to listen
to supporting a different set of assumptions than we currently use, but
I'd like to see a clear explanation of what assumptions are being made
and why they represent a useful case.
I am unsure why Sigres is significantly faster than just creating a file
system on the permanent memory and putting xlog on there.
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--
Hideyuki Kawashima (Ph.D), University of Tsukuba,
Graduate School of Systems and Information Engineering
Assistant Professor, TEL: +81-29-853-5322
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