Re: Hash Functions

On Tue, Aug 22, 2017 at 5:44 PM, amul sul <sulamul@gmail.com> wrote:

> On Fri, Aug 18, 2017 at 11:01 PM, Robert Haas <robertmhaas@gmail.com>
> wrote:
>
>> On Fri, Aug 18, 2017 at 1:12 PM, amul sul <sulamul@gmail.com> wrote:
>> > I have a small query,  what if I want a cache entry with extended hash
>> > function instead standard one, I might require that while adding
>> > hash_array_extended function? Do you think we need to extend
>> > lookup_type_cache() as well?
>>
>> Hmm, I thought you had changed the hash partitioning stuff so that it
>> didn't rely on lookup_type_cache().  You have to look up the function
>> using the opclass provided in the partition key definition;
>> lookup_type_cache() will give you the default one for the datatype.
>> Maybe just use get_opfamily_proc?
>>
>>
> Yes, we can do that for
> ​the ​
> partitioning code, but my concern is a little bit
> different.  I apologize, I wasn't clear enough.
>
> I am trying to extend hash_array & hash_range function. The hash_array and
> hash_range function calculates hash by using the respective hash function
> for
> the given argument type (i.e. array/range element type), and those hash
> functions are made available in the TypeCacheEntry via
> lookup_type_cache(). But
> in the hash_array & hash_range extended version requires a respective
> extended
> hash function for those element type.
>
> I have added hash_array_extended & hash_range_extended function in the
> attached
> patch 0001, which maintains a local copy of TypeCacheEntry with extended
> hash
> functions. But I am a little bit skeptic about this logic, any
> ​ ​
> advice/suggestions will be
> greatly appreciated.
>
>
​Instead, in the attached patch, I have modified lookup_type_cache() to
request it to get extended hash function in the TypeCacheEntry.

For that, I've introduced new flags as TYPECACHE_HASH_EXTENDED_PROC,
TYPECACHE_HASH_EXTENDED_PROC_FINFO & TCFLAGS_CHECKED_HASH_EXTENDED_PROC, and
additional variables in TypeCacheEntry structure to hold extended hash proc
information.


> The logic in the rest of the extended hash functions is same as the
> standard
> one.
>

​Same for the hash_array_extended() & hash_range_extended() function as
well.

​Regards,
Amul​