Zdenek Kotala wrote:
> By my opinion first place where tuple should be placed is:
>
> MAXALIGN(SizeOfPageHeaderData + sizeof(ItemIdData))
Yeah, but we don't enforce that directly. We enforce it by MAXALIGNing
size in PageAddItem, and with the rule that special-size is MAXALIGNed.
To put it another way, it's possible that there's an unaligned amount of
free space on a page, as returned by PageGetExactFreeSpace. But since
item size is always MAXALIGNed, it's impossible to use it all.
Come to think of it, why do we require MAXALIGN alignment of tuples? I
must be missing something, but AFAICS the widest fields in
HeapTupleHeaderData are 4-bytes wide, so it should be possible to get
away with 4-byte alignment.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
