Re: Performance Improvement by reducing WAL for Update Operation

On Friday, January 11, 2013 9:27 PM Simon Riggs wrote:
On 11 January 2013 14:24, Amit Kapila <amit.kapila@huawei.com> wrote:

>> http://archives.postgresql.org/message-id/6C0B27F7206C9E4CA54AE035729E9C3828
>> 52DE51@szxeml509-mbs
>
>> 1. However Heikki has pointed, it has some problems similar to for HOT
>> implementation and that is the reason we have done memcmp for HOT.
>> 2. Also we have found in initial readings that this doesn't have any
>> performance difference as compare to current Approach.

>OK, forget that idea.

>>> I've moved this to the next CF. I'm planning to review this one first.
>
>> Thank you.

> Just reviewing the patch now, making more sense with comments added.

>In heap_delta_encode() do we store which columns have changed? 

Not the attribute bumberwise, but offsetwise it is stored.

> Do we store the whole new column value?

Yes, please refer else part of code

+ 		else
+ 		{
+ 			data_len = new_tup_off - change_off;
+ 			if ((bp + (2 * data_len)) - bstart >= result_max)
+ 				return false;
+ 
+ 			/* Copy the modified column data to the output buffer if present */
+ 			pglz_out_add(ctrlp, ctrlb, ctrl, bp, data_len, dp);
+ 

With Regards,
Amit Kapila.