Thread: Is there a way to translate pg_amop.amopstrategy into a description?
I'm digging into GiST indexes again, and ran into a helpful script here:
(This piece has shown up in many places in various versions.) I've adapted the search a little, as I'd like to make it easier to explore available index ops:
SELECT amop.amopopr::regoperator AS operator,
iif(amop.amoppurpose = 's', 'search','order') AS purpose,
amop.amopstrategy AS stratgey_number -- I'd like to translate this into a description
FROM pg_opclass opc,
pg_opfamily opf,
pg_am am,
pg_amop amop
WHERE opc.opcname = 'gist_trgm_ops'
AND am.amname = 'gist'
AND opf.oid = opc.opcfamily
AND am.oid = opf.opfmethod
AND amop.amopfamily = opc.opcfamily
AND amop.amoplefttype = opc.opcintype;
+------------------+---------+-----------------+
| operator | purpose | stratgey_number |
+------------------+---------+-----------------+
| %(text,text) | search | 1 |
| <->(text,text) | order | 2 |
| ~~(text,text) | search | 3 |
| ~~*(text,text) | search | 4 |
| ~(text,text) | search | 5 |
| ~*(text,text) | search | 6 |
| %>(text,text) | search | 7 |
| <->>(text,text) | order | 8 |
| %>>(text,text) | search | 9 |
| <->>>(text,text) | order | 10 |
| =(text,text) | search | 11 |
+------------------+---------+-----------------+What I'm hoping for is a function like get_opt_class_strategy_description(optclass, straregy_number) I've looked at the source a bit, and it seems that there is no such function, and that it might well be difficult to implement. The strategy numbers are, as far as I can see, local to the specific opt_class, which has no requirement to label them in any particular way.Does anyone know if I'm missing something?Along the way, I did find that you can often look things up by hand in the source for specific tools, or review a lot of the strategies in one place:https://github.com/postgres/postgres/blob/edcb71258504ed22abba8cc7181d2bab3762e757/src/include/catalog/pg_amop.dat#L82It's easier to use the docs at that point.No lives hang in the balance here, but I'm hoping to learn something.Thanks for any help or clarification.
Morris de Oryx <morrisdeoryx@gmail.com> writes:
> What I'm hoping for is a function like
> get_opt_class_strategy_description(optclass, straregy_number) I've
> looked at the source a bit, and it seems that there is no such
> function, and that it might well be difficult to implement. The
> strategy numbers are, as far as I can see, local to the specific
> opt_class, which has no requirement to label them in any particular
> way.
That's correct. For btree and hash, the meanings of the strategy
numbers are determined by the index AM; but for (IIRC) all of our
other index AMs they're determined by the individual opclass. So
anything like this would have to be implemented by dedicated code
in each opclass. Perhaps that's worth doing, but it'd be a fair
amount of work.
regards, tom lane
Thanks for the confirmation. And, I'd say that this feature would go under "nice to have" rather than anything more important. Although, it would be nice.
On Thu, Aug 22, 2024 at 5:42 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
Morris de Oryx <morrisdeoryx@gmail.com> writes:
> What I'm hoping for is a function like
> get_opt_class_strategy_description(optclass, straregy_number) I've
> looked at the source a bit, and it seems that there is no such
> function, and that it might well be difficult to implement. The
> strategy numbers are, as far as I can see, local to the specific
> opt_class, which has no requirement to label them in any particular
> way.
That's correct. For btree and hash, the meanings of the strategy
numbers are determined by the index AM; but for (IIRC) all of our
other index AMs they're determined by the individual opclass. So
anything like this would have to be implemented by dedicated code
in each opclass. Perhaps that's worth doing, but it'd be a fair
amount of work.
regards, tom lane