Re: pageinspect: Hash index support

On Wed, Jan 18, 2017 at 3:24 PM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
>
>> 4.
>> +Datum
>> +hash_page_items(PG_FUNCTION_ARGS)
>> +{
>> + bytea *raw_page = PG_GETARG_BYTEA_P(0);
>>
>>
>> +Datum
>> +hash_bitmap_info(PG_FUNCTION_ARGS)
>> +{
>> + Oid indexRelid = PG_GETARG_OID(0);
>> + uint32 ovflblkno = PG_GETARG_UINT32(1);
>>
>> Is there a reason for keeping the input arguments for
>> hash_bitmap_info() different from hash_page_items()?
>>
>
> Yes, there are two reasons behind it.
>
> Firstly, we need metapage to identify the bitmap page that holds the
> information about the overflow page passed as an input to this
> function.
>

Okay, for that probably index oid is sufficient.

> Secondly, we will have to input overflow block number as an input to
> this function so as to determine the overflow bit number which can be
> used further to identify the bitmap page.
>

I think you can get that from bucket number by using BUCKET_TO_BLKNO.
You can get bucket number from page's opaque data. So, if we follow
that then you can have a prototype of a function as
hash_bitmap_info(index_oid, page bytea) which will be quite similar to
other API's exposed by this module.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com