wjones127 commented on code in PR #33694:
URL: https://github.com/apache/arrow/pull/33694#discussion_r1081979118
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cpp/src/parquet/properties.h:
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@@ -452,19 +452,39 @@ class PARQUET_EXPORT WriterProperties {
return this->disable_statistics(path->ToDotString());
}
- /// Enable integer type to annotate decimal type as below:
- /// int32: 1 <= precision <= 9
- /// int64: 10 <= precision <= 18
- /// Default disabled.
- Builder* enable_integer_annotate_decimal() {
- integer_annotate_decimal_ = true;
+ /// Enable decimal logical type with 1 <= precision <= 18 to be stored as
+ /// integer physical type.
+ ///
+ /// According to the specs, DECIMAL can be used to annotate the following
types:
+ /// - int32: for 1 <= precision <= 9.
+ /// - int64: for 1 <= precision <= 18; precision < 10 will produce a
warning.
+ /// - fixed_len_byte_array: precision is limited by the array size.
+ /// Length n can store <= floor(log_10(2^(8*n - 1) - 1)) base-10 digits.
+ /// - binary: precision is not limited, but is required. precision is not
limited,
+ /// but is required. The minimum number of bytes to store the unscaled
value
+ /// should be used.
+ ///
+ /// By default, this is DISABLED and all decimal types annotate
fixed_len_byte_array.
+ ///
+ /// When enabled, the C++ writer will use following physical types to
store decimals:
+ /// - int32: for 1 <= precision <= 9.
+ /// - int64: for 10 <= precision <= 18.
+ /// - fixed_len_byte_array: for precision > 18.
+ ///
+ /// As a consequence, decimal columns stored in integer types are more
compact
+ /// but in a risk that the parquet file may not be readable by previous
Arrow C++
+ /// versions or other implementations.
Review Comment:
FYI @pitrou
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