99 lines
3.2 KiB
Plaintext
99 lines
3.2 KiB
Plaintext
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<Chapter>
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<DocInfo>
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<AuthorGroup>
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<Author>
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<FirstName>Gene</FirstName>
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<Surname>Selkov</Surname>
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</Author>
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</AuthorGroup>
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<Date>Transcribed 1998-02-19</Date>
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</DocInfo>
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<Title>GiST Indices</Title>
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<Para>
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<Note>
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<Title>Caveat</Title>
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<Para>
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This extraction from an e-mail sent by
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<ULink url="mailto:selkovjr@mcs.anl.gov">Eugene Selkov Jr.</ULink>
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contains good information
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on GiST. Hopefully we will learn more in the future and update this information.
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- thomas
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</Para>
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</Note>
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<Para>
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Well, I can't say I quite understand what's going on, but at least
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I (almost) succeeded in porting GiST examples to linux. The GiST access
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method is already in the postgres tree (<FileName>src/backend/access/gist</FileName>).
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<Para>
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<ULink url="ftp://s2k-ftp.cs.berkeley.edu/pub/gist/pggist/pggist.tgz">Examples at Berkeley</ULink>
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come with an overview of the methods and demonstrate spatial index
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mechanisms for 2D boxes, polygons, integer intervals and text
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(see also <ULink url="http://gist.cs.berkeley.edu:8000/gist/">GiST at Berkeley</ULink>).
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In the box example, we
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are supposed to see a performance gain when using the GiST index; it did
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work for me but I do not have a reasonably large collection of boxes
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to check that. Other examples also worked, except polygons: I got an
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error doing
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<ProgramListing>
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test=> create index pix on polytmp using gist (p:box gist_poly_ops) with
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(islossy);
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ERROR: cannot open pix
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(PostgreSQL 6.3 Sun Feb 1 14:57:30 EST 1998)
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</ProgramListing>
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<Para>
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I could not get sense of this error message; it appears to be something
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we'd rather ask the developers about (see also Note 4 below). What I
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would suggest here is that someone of you linux guys (linux==gcc?) fetch the
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original sources quoted above and apply my patch (see attachment) and
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tell us what you feel about it. Looks cool to me, but I would not like
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to hold it up while there are so many competent people around.
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<Para>
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A few notes on the sources:
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<Para>
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1. I failed to make use of the original (HPUX) Makefile and rearranged
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the Makefile from the ancient postgres95 tutorial to do the job. I
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tried
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to keep it generic, but I am a very poor makefile writer -- just did
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some monkey work. Sorry about that, but I guess it is now a little
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more portable that the original makefile.
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<Para>
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2. I built the example sources right under pgsql/src (just extracted the
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tar file there). The aforementioned Makefile assumes it is one level
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below pgsql/src (in our case, in pgsql/src/pggist).
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<Para>
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3. The changes I made to the *.c files were all about #include's,
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function prototypes and typecasting. Other than that, I just threw
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away a bunch of unused vars and added a couple parentheses to please
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gcc. I hope I did not screw up too much :)
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<Para>
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4. There is a comment in polyproc.sql:
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<ProgramListing>
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-- -- there's a memory leak in rtree poly_ops!!
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-- -- create index pix2 on polytmp using rtree (p poly_ops);
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</ProgramListing>
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Roger that!! I thought it could be related to a number of
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<ProductName>Postgres</ProductName> versions
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back and tried the query. My system went nuts and I had to shoot down
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the postmaster in about ten minutes.
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<Para>
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I will continue to look into GiST for a while, but I would also
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appreciate
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more examples of R-tree usage.
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</Chapter>
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