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Re: [PATCHES] Re: Patch for JDBC timestamp problems

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Joseph Shraibman <jks(at)selectacast(dot)net>
Cc: Barry Lind <barry(at)xythos(dot)com>, pgsql-patches(at)postgresql(dot)org, pgsql-interfaces(at)postgresql(dot)org, PostgreSQL jdbc list <pgsql-jdbc(at)postgresql(dot)org>
Subject: Re: [PATCHES] Re: Patch for JDBC timestamp problems
Date: 2001-01-24 14:18:01
Message-ID: 200101241418.JAA14935@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-interfacespgsql-jdbcpgsql-patches
What was the conclusion of this discussion?  Do we leave it static?

> Barry Lind wrote:
> > 
> > Attached is a set of patches for a couple of bugs dealing with
> > timestamps in JDBC.
> > 
> > Bug#1) Incorrect timestamp stored in DB if client timezone different
> > than DB.
> > 
> > The buggy implementation of setTimestamp() in PreparedStatement simply
> > used the toString() method of the java.sql.Timestamp object to convert
> > to a string to send to the database.  The format of this is yyyy-MM-dd
> > hh:mm:ss.SSS which doesn't include any timezone information.  Therefore
> > the DB assumes its timezone since none is specified.  That is OK if the
> > timezone of the client and server are the same, however if they are
> > different the wrong timestamp is received by the server.  For example if
> > the client is running in timezone GMT and wants to send the timestamp
> > for noon to a server running in PST (GMT-8 hours), then the server will
> > receive 2000-01-12 12:00:00.0 and interprete it as 2000-01-12
> > 12:00:00-08 which is 2000-01-12 04:00:00 in GMT.  The fix is to send a
> > format to the server that includes the timezone offset.  For simplicity
> > sake the fix uses a SimpleDateFormat object with its timezone set to GMT
> > so that '+00' can be used as the timezone for postgresql.  This is done
> > as SimpleDateFormat doesn't support formating timezones in the way
> > postgresql expects.
> > 
> > Bug#2) Incorrect handling of partial seconds in getting timestamps from
> > the DB
> > 
> > When the SimpleDateFormat object parses a string with a format like
> > yyyy-MM-dd hh:mm:ss.SS it expects the fractional seconds to be three
> > decimal places (time precision in java is miliseconds = three decimal
> > places).  This seems like a bug in java to me, but it is unlikely to be
> > fixed anytime soon, so the postgresql code needed modification to
> > support the java behaviour.  So for example a string of '2000-01-12
> > 12:00:00.12-08' coming from the database was being converted to a
> > timestamp object with a value of 2000-01-12 12:00:00.012GMT-08:00.  The
> > fix was to check for a '.' in the string and if one is found append on
> > an extra zero to the fractional seconds part.
> > 
> > Bug#3) Performance problems
> > 
> > In fixing the above two bugs, I noticed some things that could be
> > improved.  In PreparedStatement.setTimestamp(),
> > PreparedStatement.setDate(), ResultSet.getTimestamp(), and
> > ResultSet.getDate() these methods were creating a new SimpleDateFormat
> > object everytime they were called.  To avoid this unnecessary object
> > creation overhead, I changed the code to use static variables for
> > keeping a single instance of the needed formating objects.
> > Also the code used the + operator for string concatenation.  As everyone
> > should know this is very inefficient and the use of StringBuffers is
> > prefered.
> > 
> 
> While the java spec says that a+b+c should be converted into
> a.concat(b.toString()).concat(c.toString())
>  probably every single java compiler (including javac) uses
> StringBuffers.  The only case where it is an advantage to use your own
> stringBuffer is in a case like:
> 
> StringBuffer sb = new StringBuffer("blah");
> sb.append(a+b+c);
> 
> Since that would create a temporary StringBuffer to calculate a+b+c just
> to append to the original sb it it might be better to explictly append
> a,b,and c.
> 
> 
> Using static SimpleDateFormats will probably not cause threading
> issues.  Common sense says that if the set methods are never called on
> them there will be no state change that my cause sync problems.  But the
> spec doesn't garuntee it.  Personally I would have no problem using
> static SimpleDateFormats if this were my code.
> 
> 
> 
> -- 
> Joseph Shraibman
> jks(at)selectacast(dot)net
> Increase signal to noise ratio.  http://www.targabot.com
> 


-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

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