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Re: [BUGS] no way in LargeObject API to detect short read?

From: Barry Lind <barry(at)xythos(dot)com>
To: Peter T Mount <peter(at)retep(dot)org(dot)uk>
Cc: PostgreSQL jdbc list <pgsql-jdbc(at)postgresql(dot)org>
Subject: Re: [BUGS] no way in LargeObject API to detect short read?
Date: 2001-01-26 23:37:50
Message-ID: 3A720A4E.D237F47B@xythos.com (view raw or flat)
Thread:
Lists: pgsql-bugspgsql-jdbc
Peter,

Given the current implementation of size(), I don't think this is a good
solution to the problem at hand.  Since size() is an expensive call
(especially on large files), using it in this way wouldn't be a
performant solution.  Using size() also requires additional round trips
to the database to get this information.  There needs to be a better
solution that doesn't require the additional overhead.

thanks,
--Barry

Peter T Mount wrote:
> 
> Hmmm, what's the performance issues with this? Is there going to be a problem
> with very large LargeObject's?
> 
> Quoting "Paul M. Aoki" <aoki(at)acm(dot)org>:
> 
> > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > > Anyone able to fix this?
> >
> > here's a hack we've been using in-house (written by Jun Gabayan,
> > <jgabayan(at)pahv(dot)xerox(dot)com>).
> >
> > you may not like the style but it's a stab at a solution.
> > --
> >  Paul M. Aoki / Xerox Palo Alto Research Center / 3333 Coyote Hill Road
> >  aoki(at)acm(dot)org / Computer Science Laboratory     / Palo Alto, CA
> > 94304-1314
> >
> > Index: LargeObject.java
> > ===================================================================
> > RCS file:
> > /project/placeless/cvsroot/placeless2/src/org/postgresql/largeobject/LargeObje
> ct.java,v
> > retrieving revision 1.1
> > retrieving revision 1.3
> > diff -r1.1 -r1.3
> > 64c64,67
> > <
> > ---
> > >
> > >   private int pos = 0; //current position
> > >   private int size = 0;
> > >
> > 85a89,90
> > >     pos = tell();
> > >     size = size();
> > 102a108
> > >     if(fd == 0) return;
> > 105a112
> > >     fd = 0;
> > 118a126,132
> > >         // calculate available data to read to avoid reading pass the
> > end
> > >         // to avoid an exception
> > >         pos = tell();
> > >         int avail = size - pos;
> > >         if(avail == 0) return null;
> > >         if(avail < len) len = avail;
> > >         try {
> > 123c137,141
> > <
> > ---
> > >         }catch(SQLException se) {
> > >           System.out.println("***LargeObject.read: Caught
> > SQLException: " + se.getMessage());
> > >           return null;
> > >         }
> > >
> > 157c175
> > <   public void read(byte buf[],int off,int len) throws SQLException
> > ---
> > >   public int read(byte buf[],int off,int len) throws SQLException
> > 159c177,180
> > <     System.arraycopy(read(len),0,buf,off,len);
> > ---
> > >     byte mybuf[] = read(len);
> > >     int sz = (mybuf != null) ? mybuf.length : -1; //must return -1 for
> > end of data
> > >     if(sz > 0) System.arraycopy(mybuf,0,buf,off,sz);
> > >     return sz;
> >
> 
> --
> Peter Mount peter(at)retep(dot)org(dot)uk
> PostgreSQL JDBC Driver: http://www.retep.org.uk/postgres/
> RetepPDF PDF library for Java: http://www.retep.org.uk/pdf/

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