Bruce Momjian wrote:
> We have two problems. First, indexes are not used with OR's. This is a
> serious problem, with no good workaround. I have looked at the code,
> and there are two places that need changes. First, there is much code
> in the optimizer to handle OR's, but it was turned off because it did
> not work. There is also no support in the executor to handle multiple
> OR values when using indexes. I have fixed the optimizer so it can now
> identify OR clauses and handle them properly:
> test=> explain select * from test where x=3 or x=4;
> NOTICE: equal: don't know whether nodes of type 200 are equal
> NOTICE: QUERY PLAN:
> Index Scan using i_test on test (cost=4.10 size=1 width=4)
> As you can see, I am getting a NOTICE I have to check into. Also, the
> executor is only returning the FIRST of the OR conditions, because I
> have not yet added code to nodeIndexscan.c to handle multiple values.
> This code is not installed in the main source tree. I will complete my
> cleanups and tests, and install it. I may need help with
> nodeIndexscan.c. My idea is to hook up multiple ScanKeys, and to move
> on to the next one when the first finishes. Perhaps someone (Vadim?)
> could help as I am a little lost in how to do that. Pointers to similar
> code would help.
* IndexScanState information
* IndexPtr current index in use
* NumIndices number of indices in this scan
* ScanKeys Skey structures to scan index rels
* NumScanKeys array of no of keys in each Skey struct
- some support is already in Executor!
Functions in nodeIndexscan.c also handle this.
Currently, IndexPtr is ALWAYS ZERO - so you have to add code to
switch to the next index after NULL is returned by index_getnext()
Note that different indices (of the same table) may be used
in single scan (x = 3 or y = 1)!
The most complex stuff to be implemented for something
like (x = 3 or y = 1) is to check that for tuples, fetched
by second index sub-scan, x IS NOT EQUAL 3!
Maybe IndexScan->indxqual can help you...
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