Re: numeric/decimal docs bug?
От | Bruce Momjian |
---|---|
Тема | Re: numeric/decimal docs bug? |
Дата | |
Msg-id | 200204130137.g3D1bY213251@candle.pha.pa.us обсуждение исходный текст |
Ответ на | Re: numeric/decimal docs bug? (Tatsuo Ishii <t-ishii@sra.co.jp>) |
Список | pgsql-hackers |
Tatsuo Ishii wrote: > > Jan Wieck wrote: > > > > The hard limit is certainly no more than 64K, since we store these > > > > numbers in half of an atttypmod. In practice I suspect the limit may > > > > be less; Jan would be more likely to remember... > > > > > > It is arbitrary of course. I don't recall completely, have to > > > dig into the code, but there might be some side effect when > > > mucking with it. > > > > > > The NUMERIC code increases the actual internal precision when > > > doing multiply and divide, what happens a gazillion times > > > when doing higher functions like trigonometry. I think there > > > was some connection between the max precision and how high > > > this internal precision can grow, so increasing the precision > > > might affect the computational performance of such higher > > > functions significantly. > > > > Oh, interesting, maybe we should just leave it alone. > > So are we going to just fix the docs? OK, I have updated the docs. Patch attached. I have also added this to the TODO list: * Change NUMERIC to enforce the maximum precision, and increase it -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026 Index: datatype.sgml =================================================================== RCS file: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v retrieving revision 1.87 diff -c -r1.87 datatype.sgml *** datatype.sgml 3 Apr 2002 05:39:27 -0000 1.87 --- datatype.sgml 13 Apr 2002 01:26:54 -0000 *************** *** 506,518 **** <title>Arbitrary Precision Numbers</title> <para> ! The type <type>numeric</type> can store numbers of practically ! unlimited size and precision, while being able to store all ! numbers and carry out all calculations exactly. It is especially ! recommended for storing monetary amounts and other quantities ! where exactness is required. However, the <type>numeric</type> ! type is very slow compared to the floating-point types described ! in the next section. </para> <para> --- 506,517 ---- <title>Arbitrary Precision Numbers</title> <para> ! The type <type>numeric</type> can store numbers with up to 1,000 ! digits of precision and perform calculations exactly. It is ! especially recommended for storing monetary amounts and other ! quantities where exactness is required. However, the ! <type>numeric</type> type is very slow compared to the ! floating-point types described in the next section. </para> <para>
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