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Re: Some comments about Julian Dates and possible bug. Please provide feedback.

From: Leslie S Satenstein <lsatenstein(at)yahoo(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>, Postgres documentation <pgsql-docs(at)postgresql(dot)org>
Subject: Re: Some comments about Julian Dates and possible bug. Please provide feedback.
Date: 2010-12-29 17:38:36
Message-ID: 489318.10800.qm@web110704.mail.gq1.yahoo.com (view raw or flat)
Thread:
Lists: pgsql-docs
Good morning Robert

I presume that you are the acting project manager, in the sense of vetting changes or commentary.  The pdf guide has only one statement concerning julian dates.  I feel that more is required.

Julian dates are used as follows.

Working days between two dates is (the difference of the day numbers * 5/7) , with minor adjustment for rounding and weekend start-end considerations. 

Julian date conversion is used for this type of calculation.  It would be nice to see more in the manual about Julian dates, such as tests if a day is a weekend day, or to determine the day of the week for a specific Gregorian calendar date and vice-versa.

Regarding the julian bug(let), I will raise it as a comment on the code buglist.

 


------------------

Regards  
 Leslie
 Mr. Leslie Satenstein

 
mailto:lsatenstein(at)yahoo(dot)com
mailto leslie(dot)satenstein(at)itbms(dot)biz / leslies(at)itbms(dot)biz
www.itbms.biz
 


--- On Wed, 12/29/10, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:

> From: Robert Haas <robertmhaas(at)gmail(dot)com>
> Subject: Re: [DOCS] Some comments about Julian Dates and possible bug. Please provide feedback.
> To: "Leslie S Satenstein" <lsatenstein(at)yahoo(dot)com>
> Cc: "pgsql-docs" <pgsql-docs(at)postgresql(dot)org>
> Date: Wednesday, December 29, 2010, 6:58 AM
> On Mon, Dec 27, 2010 at 9:23 PM,
> Leslie S Satenstein
> <lsatenstein(at)yahoo(dot)com>
> wrote:
> > I found the Julian date code that is programmed in
> Postgres, to be accurate and fast except for one situation.
> But, I do have one or two questions. 1) Which calendar is
> being used?
> >
> > In the Gregorian Calendar,  January 1, 0001 is lowest
> positive date.
> > The day before 1/1/0001, according to the Gregorian
> calendar is December 31,-0001 in which the year has a value
> of negative one --- there is no zero year in the Gregorian
> Calendar. (zero year is an error)
> >
> > I tested and found the algorithm in Postgres to have
> the day before January 1,0001 calculating as December
> 31,0000 even though the world calculates the day before
> January 1,0001 as December 31,-0001.
> >
> > 2) Is the algorithm in Postgres correct?  I think
> not, as the calculations for the difference in days between
> January 1, 0001 and December 31,-0001 is not 367 days, but
> just the value 1.
> >
> > To convert the code to work with the Gregorian
> calendar takes two fixes to two sub-routines. Each fix is
> two lines of C code.
> >
> > I have tested the PG Date C language routines
> with/without my fix, starting with the year around -4713 to
> several centuries into the future. As long as both versions
> calculate Julian dates that are later than 1/1/0001, both
> the PG and my fixed versions respecting Gregorian algorithms
> produce identical results.
> >
> > 3) Does PG want to fully follow the Gregorian Calendar
> rule?  If so,
> > 4) do they want my one patch with two fixes6
> 
> This seems like it'd be more appropriate for pgsql-bugs or
> pgsql-hackers rather than here.  I can't really figure
> out exactly
> what change you're proposing, so I'm not entirely sure
> whether it's
> right or wrong.  Perhaps you could post your patch,
> and some examples.
> 
> -- 
> Robert Haas
> EnterpriseDB: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
> 
> -- 
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