WIP: New Page API

I finished first prototype of new page API. It contains several new functions like:

Pointer PageGetUpperPointer(Page page);

void PageClearPrunable(Page page);
bool PageIsComprimable(Page page);

void PageReserveLinp(Page page);
void PageReleaseLinp(Page page);

LocationIndex PageGetLower(Page page);
LocationIndex PageGetUpper(Page page);
LocationIndex PageGetSpecial(Page page);
void PageSetLower(Page page, LocationIndex lower);
void PageSetUpper(Page page, LocationIndex lower);

Page PageGetTempPage(Page page, bool copy);
Page PageGetTempPageCopySpecial(Page page);
void PageRestoreTempPage(Page tempPage, Page oldPage);

Size PageGetSpecialSize(Page page);
Size PageGetDataSize(Page page);

bool PageLayoutIsValid(Page page);

The main point of the new API is to handle multi page layout versions. The
current implementation don't uses any speed optimization and performance gap is
about 5% (big thanks to Paul van den Bogaard for benchmarking). Finally I plan
to implement hottest function like macro (or inline fn ;-) ) and because most
structure members are located on same place I will remove extra switch in the code.

I also grab number of calls by DTrace and I got following result:

<snip>
PageGetHeapFreeSpace 984
PageGetSpecialSize 1170
PageGetFreeSpace 1200
PageGetExactFreeSpace 1399
PageGetUpper 1419
PageGetLower 1618
PageGetLSN 2936
PageGetMaxOffsetNumber 5504
PageGetSpecialPointer 13534
PageGetItemId 71074
PageGetItem 76629

I plan to remove PageGetItemId and replace it with any other function like
PageGetHeapTuple and so on. The reason is that ItemId flags has been changed
between version 3 and 4. And on many times it is called like

itemId = PageGetItemId();
PageGetItem(itemId);

I'm also thinking about add following function:

PageSetXLOG(page,TLI,LSN) - it should replace PageSetLSN();PageSetTLI();
sequence in code

I'm not happy with PageSetLower() function which is used in nbtree, but no idea
yet how to improve it.

Please, let me know your comments. I attached prototype patch.

Thanks Zdenek

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Zdenek Kotala Sun Microsystems
Prague, Czech Republic http://sun.com/postgresql