PostgreSQL version:

extra_float_digits

This parameter adjusts the number of digits used for textual output of floating-point values, including float4, float8, and geometric data types.

If the value is 1 (the default) or above, float values are output in shortest-precise format; see datatype-float. The actual number of digits generated depends only on the value being output, not on the value of this parameter. At most 17 digits are required for float8 values, and 9 for float4 values. This format is both fast and precise, preserving the original binary float value exactly when correctly read. For historical compatibility, values up to 3 are permitted.

If the value is zero or negative, then the output is rounded to a given decimal precision. The precision used is the standard number of digits for the type (FLT_DIG or DBL_DIG as appropriate) reduced according to the value of this parameter. (For example, specifying -1 will cause float4 values to be output rounded to 5 significant digits, and float8 values rounded to 14 digits.) This format is slower and does not preserve all the bits of the binary float value, but may be more human-readable.

The meaning of this parameter, and its default value, changed in PostgreSQL 12; see datatype-float for further discussion.

Recommendations

Only significant for applications which do a lot of float calculations, like scientific databases.

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