> Legacy apps, Bruce. Sometimes you come across tables with ten fields in the
> index. I'm working on a (fairly specialised) system now where the primary
> key of one of the tables has twenty-four fields in it. It is a summary
> table, and probably not the best design, but that's the way it is, and I
> have to live with it. Unfortunately, because we don't have a database that
> can have that many fields in a key, we have to construct manual indices in
> code. Even Oracle (which is what we are using) only goes up to about 21 or
> something. However, if you are going to summarise heavily, then the number
> of fields in your primary key can get quite large.
> How difficult would it be to make the number of fields in an index unlimited
> (or arbitrarily large). Perhaps there could be a compile-time variable
> which is defaulted to 7, but which can be increased using the configure
> script (./configure --with-index-fields=24). I realise that there are
> performance issues, but that's a trade off that only the system designers
> can make.
There is a special oid8 type that holds eight oids the represent the
index entries. We would have to expand that field to a larger value. I
don't believe there is any real reason we have to limit it to eight. We
don't do any other fancy stuff with it. The only other issue is that
all indexes will have to use the maximum space. We could make it a
varlena() field, and do it that way.
We have not had any real demand for more than eight, but I can see your
point. I will put it on the TODO list.
--
Bruce Momjian | http://www.op.net/~candle
maillist@candle.pha.pa.us | (610) 853-3000
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