On Fri, 6 Jun 1997, Vadim B. Mikheev wrote:
> Well, I hope that bug reported by Michael is old bug.
>
> Simple example:
>
> bt=> create table test (x text);
> CREATE
> bt=> create index test_i on test (x);
> CREATE
> bt=> insert into test values ('0');
> INSERT 449464
> bt=> copy test from '/home/postgres/My/Btree/BUG/B';
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 400 records with '12345'
> COPY
> bt=> vacuum verbose test;
> NOTICE:Rel test: Pages 4: Changed 4, Reapped 0, Empty 0, New 0; Tup 401: Vac 0, Crash 0, UnUsed 0, MinLen 53, MaxLen
57;Re-using: Free/Avail. Space 0/0; EndEmpty/Avail. Pages 0/0. Elapsed 0/0 sec.
> NOTICE:Ind test_i: Pages 5; Tuples 400. Elapsed 0/0 sec.
> NOTICE:Ind test_i: NUMBER OF INDEX' TUPLES (400) IS NOT THE SAME AS HEAP' (401)
> VACUUM
>
> (I've got the same results under 6.0)
>
> : splitting occures when there are 1 '0' and 291 '12345' on the first btree
> page - PageGetFreeSpace(page) returns 0. Following duplicates handling
> rules, '0' has to go on the 1st page and 291 '12345' - on the new page.
> + new '12345' item will also go on the new page!!!
> But there is no space for '12345' here: we got rid of '0' - 8 bytes of
> data - and want to add 16 bytes (double aligning).
> New item wasn't added, silently. Check added now, so you'll
> get FATAL...
>
> There is no time to fix it now. I'll try to do it latter.
>
> ...Original Lehman and Yao algorithm doesn't allow duplicates at all.
> Old team added some hacks... and we have to add yet more...
>
> BTW, there shouldn't be problems in using btree for variable
> length attributes if there are no duplicates... Michael, are there
> duplicates in your table ?
>
> Marc, did you use btree for variable length attributes?
> Do you have duplicates ?
Assuming you mean varchar()? No, all my attributes are of text...
but, then again, I guess that means variable lenght, eh? :( Yes, my
indices are based on variable length attributes...
As for duplicates...the most likely are duplicates for each
'indexed field'..
Marc G. Fournier
Systems Administrator @ hub.org
primary: scrappy@hub.org secondary: scrappy@{freebsd|postgresql}.org
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