Re: Reviewing freeze map code

On Mon, Jul 4, 2016 at 5:44 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> On Sat, Jul 2, 2016 at 12:34 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> On Fri, Jul 1, 2016 at 7:52 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>>> On Fri, Jul 1, 2016 at 11:12 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>>>
>>>> Why do you think IndexOnlyScan will return wrong result? If the
>>>> server crash in the way as you described, the transaction that has
>>>> made modifications will anyway be considered aborted, so the result of
>>>> IndexOnlyScan should not be wrong.
>>>>
>>>
>>> Ah, you're right, I misunderstood.
>>>
>>> Attached updated patch incorporating your comments.
>>> I've changed it so that heap_xlog_lock clears vm flags if page is
>>> marked all frozen.
>>>
>>
>> I think we should make a similar change in heap_lock_tuple API as
>> well.
>> Also, currently by default heap_xlog_lock tuple tries to clear
>> the visibility flags, isn't it better to handle it as we do at all
>> other places (ex. see log_heap_update), by logging the information
>> about same.
>
> I will deal with them.
>
>> Though, it is important to get the patch right, but I feel in the
>> meantime, it might be better to start benchmarking. AFAIU, even if
>> change some part of information while WAL logging it, the benchmark
>> results won't be much different.
>
> Okay, I will do the benchmark test as well.
>

I measured the thoughput and the output quantity of WAL with HEAD and
HEAD+patch(attached) on my virtual environment.
I used pgbench with attached custom script file which sets 3200 length
string to the filler column in order to make toast data.
The scale factor is 1000 and pgbench options are, -c 4 -T 600 -f toast_test.sql.
After changed filler column to the text data type I ran it.

* Throughput
HEAD : 1833.204172
Patched : 1827.399482

* Output quantity of WAL
HEAD : 7771 MB
Patched : 8082 MB

The throughput is almost same, but the ouput quantity of WAL is
slightly increased. (about 4%)

Regards,

--
Masahiko Sawada