Scott Carey: > You are CPU bound. > > 30% of 4 cores is greater than 25%. 25% is one core fully > used. I have measured the cores separately. Some of them reached 30%. I am not CPU bound here. > The postgres compression of data in TOAST is > probably the problem. I'm assuming its doing Gzip, and at > the default compression level, which on random data will > be in the 15MB/sec range. I don't know if TOAST will do > compression at a lower compression level. Hm. I use 'bytea' (see original posting) and SET STORAGE EXTERNAL for this column which switches of the compression AFAIK. I was doing this to measure the raw performance and may not be able to use compression later in real scenario. BTW: In the initial tests I used 200 blocks of 4 MB bytea which is the real scenario; later on I was using 10 times 80MB each just to reduce the number of INSERT commands and to make it easier to find the performance problem. > Is your data typically random or incompressible? If it is > compressible then your test should be changed to reflect > that. Unfortunatelly I can't say much yet. Of course, in case compression makes sense and fits the CPU performance I will use it. > If I am wrong, you are I/O bound Yes. This is the first half of what we found out now. > -- this will show up in > windows Performance Monitor as "Disk Time (%)" -- which > you can get on a per device or total basis, along with i/o > per second (read and/or write) and bytes/sec metrics. Yes, I am using this tool. However, the deeper question is (sounds ridiculous): Why am I I/O bound *this much* here. To recall: The write performance in pg is about 20-25% of the worst case serial write performance of the disk (and only about 8-10% of the best disk perf) even though pg_xlog (WAL) is moved to another disk, only 10 simple INSERT commands, a simple table of 5 columns (4 unused, one bytea) and one index for OID, no compression since STORAGE EXTERNAL, ntfs tweaks (noatime etc), ... > To prove that you are CPU bound, split your test in half, > and run the two halves at the same time. If you are CPU > bound, then your bytes/sec performance will go up > significantly, along with CPU usage. Done already (see earlier posting). I am not CPU bound. Speed was the same. Thank You for the detailed reply. Felix -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
