Обсуждение: README of hash index

Currently README of hash module contain algorithms written in below form.

The insertion algorithm is rather similar:

pin meta page and take buffer content lock in shared mode
loop:
compute bucket number for target hash key
release meta page buffer content lock
if (correct bucket page is already locked)
break
release any existing bucket page lock (if a concurrent split happened)
take heavyweight bucket lock in shared mode
retake meta page buffer content lock in shared mode
-- (so far same as reader)
release pin on metapage
..
..

I have mostly updated them in the patches I have proposed to improve
hash index.  However, each time I try to update them, I find that it
is easy to follow the code than to read and understand the existing
algorithm written in above form from README.

Do others find it useful to maintain the algorithms in above form?

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

On Fri, Sep 16, 2016 at 04:50:53PM +0530, Amit Kapila wrote:
> Currently README of hash module contain algorithms written in below form.
> 
> The insertion algorithm is rather similar:
> 
> pin meta page and take buffer content lock in shared mode
> loop:
> compute bucket number for target hash key
> release meta page buffer content lock
> if (correct bucket page is already locked)
> break
> release any existing bucket page lock (if a concurrent split happened)
> take heavyweight bucket lock in shared mode
> retake meta page buffer content lock in shared mode
> -- (so far same as reader)
> release pin on metapage
> ..
> ..
> 
> I have mostly updated them in the patches I have proposed to improve
> hash index.  However, each time I try to update them, I find that it
> is easy to follow the code than to read and understand the existing
> algorithm written in above form from README.
> 
> Do others find it useful to maintain the algorithms in above form?
> 

Hi Amit,

Speaking for myself, I think it does help to have a text description
of the algorithm to use as a guide while trying to understand the code.
For beginners (me), it is not always obvious what a section of code is
doing.

Regards,
Ken

On Fri, Sep 16, 2016 at 9:56 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
> On Fri, Sep 16, 2016 at 4:20 AM, Amit Kapila <amit.kapila16@gmail.com>
> wrote:
>>
>> Currently README of hash module contain algorithms written in below form.
>>
>> The insertion algorithm is rather similar:
>>
>> pin meta page and take buffer content lock in shared mode
>> loop:
>> compute bucket number for target hash key
>> release meta page buffer content lock
>> if (correct bucket page is already locked)
>> break
>> release any existing bucket page lock (if a concurrent split happened)
>> take heavyweight bucket lock in shared mode
>> retake meta page buffer content lock in shared mode
>> -- (so far same as reader)
>> release pin on metapage
>> ..
>> ..
>>
>> I have mostly updated them in the patches I have proposed to improve
>> hash index.  However, each time I try to update them, I find that it
>> is easy to follow the code than to read and understand the existing
>> algorithm written in above form from README.
>>
>> Do others find it useful to maintain the algorithms in above form?
>
>
> I think that having them all condensed into one place makes it easier to
> think through the locking models to decide if there might be races or
> deadlocks.  If you only care about the algorithm for inserting in isolation,
> I agree reading the code might be better.
>


Thanks Jeff and Ken for the inputs.  I will keep the algorithms
updated in README of hash index.


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