Just as my 2 cents to the proposed idea. I want to demonstrate that the proposed idea is very relevant for the

I recently did an migration from PG 8.1 to PG 8.2. During that time I was dumping the 2TB database with several very wide tables (having ~ 200 columns). And I saw that on my pretty powerful server with 8Gb RAM, Itanium2 procesor,large RAID which can do I/O at 100Mb/sec the performance of pg_dump was CPU limited, and the read speed of the tables was 1-1.5mb/sec (leading to 2 week dumping time).

I was very surprised by these times, and profiled postgres to check the reason of that:
here is the top of gprof:
  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
 60.72     13.52    13.52  6769826     0.00     0.00  nocachegetattr
 10.58     15.88     2.36  9035566     0.00     0.00  CopyAttributeOutText
  7.22     17.49     1.61 65009457     0.00     0.00  CopySendData
  6.34     18.90     1.41        1     1.41    22.21  CopyTo

So the main slow-down of the process was all this code recomputing the boundaries of the columns.... I checked that by removing one tiny varchar column and COALESCING all NULLs, and after that the performance of pg_dumping increased by more than a factor of 2!

I should have reported that experience earlier... but I hope that my observations can be useful in the context of the Phil's idea.


Sergey E. Koposov
Max Planck Institute for Astronomy/Cambridge Institute for Astronomy/Sternberg 
Astronomical Institute
Tel: +49-6221-528-349
Web: http://lnfm1.sai.msu.ru/~math

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