Re: CLUSTER can change t_len

On 09.11.2010 15:57, Greg Stark wrote:
> On Tue, Nov 9, 2010 at 10:20 AM, Heikki Linnakangas
> <heikki.linnakangas@enterprisedb.com>  wrote:
>>>
>>> We have a comment /* be conservative */ in the function, but I'm not sure
>>> we actually need the MAXALIGN. However, there would be almost no benefits
>>> to keep t_len in small value because we often treat memory in MAXALIGN
>>> unit.
>>
>> Hmm, the conservatism at that point affects the free space calculations. I'm
>> not sure if it makes any difference in practice, but I'm also not sure it
>> doesn't. pd_upper is always MAXALIGNed, but pd_lower is not.
>>
>> This would be more in line with what the main heap_insert code does:
>
> Doesn't this cause assertion failures in heap_fill_tuple when the data
> size isn't what's expected? I guess we never actually use the t_len
> for later tuple reconstructions, we just recompute the needed size?

Right, the length from t_len or the item pointer is never passed to 
heap_fill_tuple.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com