"Stephen R. van den Berg" <s...@cuci.nl> writes:
> What seems to be hurting the most is the 1MB upper limit. What is the
> rationale behind that limit?
The argument was that compressing/decompressing such large chunks would
require a lot of CPU effort; also it would defeat attempts to fetch
subsections of a large string. In the past we've required people to
explicitly "ALTER TABLE SET STORAGE external" if they wanted to make
use of the substring-fetch optimization, but it was argued that this
would make that more likely to work automatically.
I'm not entirely convinced by Alex' analysis anyway; the only way
those 39 large values explain the size difference is if they are
*tremendously* compressible, like almost all zeroes. The toast
compressor isn't so bright that it's likely to get 10X compression
on typical data.
regards, tom lane
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