Re: Reviewing freeze map code

On Fri, Jul 1, 2016 at 11:12 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Thu, Jun 30, 2016 at 8:10 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> On Thu, Jun 30, 2016 at 3:12 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>> On Thu, Jun 30, 2016 at 9:13 AM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>>>> On 2016-06-30 08:59:16 +0530, Amit Kapila wrote:
>>>>> On Wed, Jun 29, 2016 at 10:30 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>>>>> > On 2016-06-29 19:04:31 +0530, Amit Kapila wrote:
>>>>> >> There is nothing in this record which recorded the information about
>>>>> >> visibility clear flag.
>>>>> >
>>>>> > I think we can actually defer the clearing to the lock release?
>>>>>
>>>>> How about the case if after we release the lock on page, the heap page
>>>>> gets flushed, but not vm and then server crashes?
>>>>
>>>> In the released branches there's no need to clear all visible at that
>>>> point. Note how heap_lock_tuple doesn't clear it at all. So we should be
>>>> fine there, and that's the part where reusing an existing record is
>>>> important (for compatibility).
>>>>
>>>
>>> For back branches, I agree that heap_lock_tuple is sufficient,
>>
>> Even if we use heap_lock_tuple, If server crashed after flushed heap
>> but not vm, after crash recovery the heap is still marked all-visible
>> on vm.
>
> So, in this case both vm and page will be marked as all_visible.
>
>> This case could be happen even on released branched, and could make
>> IndexOnlyScan returns wrong result?
>>
>
> 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.

Regards,

--
Masahiko Sawada