Re: Best way to scan on-disk bitmaps

If people have GIST TODOs, please post them.

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Teodor Sigaev wrote:
> About page splitting algorithm in GiST in multikey case. For the beginning, page 
> is splitted by calling pickSplit method of key of first column (pickSplit method 
> is defined for opclass and it is a user function), then it try to find equal 
> values  of first column in left and right pages ( gist.c lines 1264-1901 ). If 
> it is, then GiST core will try to resort tuples with first equal keys between 
> left and right pages using penalty method for second and higher column's key. If 
> it's not, it leave pages untouched. But unions for parent page of second and 
> higher column's keys will be formed.
> 
> So, if index is defined as 'using gist (a,b,c)' then, in principle, GiST index 
> can speed up queries like 'a=V1 and c=V2'.  But it will not usable for queries 
> ( b=V3 and c=V2 ). By the way, instead of '=' operation may be used other 
> operations. Number of supported operations by GiST is indefinite unlike, for 
> example, btree which supported only five: <, <=, =, =>, >.
> 
> 
> 
> -- 
> Teodor Sigaev                                   E-mail: teodor@sigaev.ru
>                                                     WWW: http://www.sigaev.ru/
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 9: the planner will ignore your desire to choose an index scan if your
>       joining column's datatypes do not match
> 

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