Pierre-
I agree with your observation of float <-> text conversion costs, but in
this case Dan is talking about storing the raw float data (ie: 4 bytes
per float) in a bytea array so there is only the conversion from java
float[n] to java byte[4*n] which is not nearly as costly as float <->
text conversion (especially if you leave it in architecture byte order).
Nick
If the data are stored as a byte array but retrieve into a ResultSet,
the unpacking time goes up by an order of magnitude and the
observed total throughput is 25 MB/s. If the data are stored in a
Postgres float array and unpacked into a byte stream, the
observed throughput is 20 MB/s.
float <-> text conversions are very slow, this is in fact due to the
mismatch between base-2 (IEEE754) and base-10 (text) floating point
representation, which needs very very complex calculations.
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