<para>

When <type>timestamp</> values are stored as eight-byte integers

(currently the default), microsecond precision is available over

the full range of values. When <type>timestamp</> values are

stored as double precision floating-point numbers instead (a

deprecated compile-time option), the effective limit of precision

might be less than 6. <type>timestamp</type> values are stored as

seconds before or after midnight 2000-01-01. When

<type>timestamp</type> values are implemented using floating-point

numbers, microsecond precision is achieved for dates within a few

the full range of values. In this case, the internal representation

is the number of microseconds before or after midnight 2000-01-01.

When <type>timestamp</> values are stored as double precision

floating-point numbers (a deprecated compile-time option), the

internal representation is the number of seconds before or after

midnight 2000-01-01. With this representation, the effective limit

of precision might be less than 6; in practice,

microsecond precision is achieved for dates within a few

years of 2000-01-01, but the precision degrades for dates further

away. Note that using floating-point datetimes allows a larger

range of <type>timestamp</type> values to be represented than