[HACKERS] HeapTupleHeader withoud oid
We have been discussing heap tuple header changes for a while now.
Here is my proposal for omitting the oid, when it is not needed:
First let's eliminate t_oid from HeapTupleHeaderData.
Then add the oid to the end of the structure, if and only if it is
needed. The tricky part here is that there is a variable length field
(t_bits) and the oid has to be properly aligned.
This pseudo code snippet illustrates what I plan to do:
len = offsetof(HeapTupleHeaderData, t_bits); /* 23 */
if (hasnulls) {
len += BITMAPLEN(NumberOfAttributes);
}
if (hasoid) {
len += sizeof(Oid);
}
len = MAXALIGN(len);
hoff = len;
oidoff = hoff - sizeof(Oid);
#define HeapTupleHeaderGetOid(hth) \
( *((Oid *)((char *)(hth) + (hth)-t_hoff - sizeof(Oid))) )
And this is how the structure would look like:
1 2 3
0 4 0 0 34 78 2
now -fix-.x___X___
+oid -fix-.x___ MAXALIGN 4
+oid -fix-.X___ MAXALIGN 8
-oid -fix-.X___
1:
now -fix-bx___X___
+oid -fix-bx___ MAXALIGN 4
+oid -fix-bX___ MAXALIGN 8
-oid -fix-bX___
2:
now -fix-bb...X___
+oid -fix-bb...X___ MAXALIGN 4 und 8
-oid -fix-bb...x___X___
3 4
6: 2 6 0
now -fix-bb...x___X___
+oid -fix-bb...x___ MAXALIGN 4
+oid -fix-bb...X___ MAXALIGN 8
-oid -fix-bb...X___
where
-fix- fixed sized part without oid, 23 bytes
oid, 4 bytes
b one bitmap byte
. one padding byte
x start of data area (= hoff) with 4-byte-alignment
X start of data area (= hoff) with 8-byte-alignment
Bytes saved on architectures with 4/8 byte alignment:
hoffbytes
natts bitmaplen hoff72 oidoff woosaved
0 28/32 2424/244/8
1-81 28/32 2424/244/8
9-40 2-532/32 2828/324/0
41-72 6-936/40 3232/324/8
As a first step I've already posted a patch that eliminates direct
access to t_oid. The final patch will change not much more than the
getter and setter macros.
Problems I have identified so far:
. heap_formtuple needs a parameter bool withoid
. Does heap_addheader *always* create a header with oid?
. Have to check heap_xlog_ routines
. Occasionally a heap tuple header is copied by memmove.
Comments?
Servus
Manfred
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Re: [HACKERS] HeapTupleHeader withoud oid
Manfred Koizar [EMAIL PROTECTED] writes: . Does heap_addheader *always* create a header with oid? No. regards, tom lane ---(end of broadcast)--- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
Re: [HACKERS] HeapTupleHeader withoud oid
Manfred Koizar [EMAIL PROTECTED] writes: Here is my proposal for omitting the oid, when it is not needed: I do not think you can make this work unless has oids is added to TupleDescs. There are too many places where tuples are manipulated with only a tupdesc for reference. It might also be necessary to add a has oid bit to t_infomask, so that a tuple's OID can be fetched with *no* outside information, but I'd prefer to avoid that if possible. I think adding a tupledesc parameter to heap_getsysattr might be enough to avoid it. I'd suggest reworking your Wrap access to Oid patch, which currently increases instead of reducing the dependency on access to a Relation for the tuple. Also, you could be a little more conservative about adding Asserts --- those are not free, at least not from a development point of view, so I object to adding multiple redundant Asserts in hotspot routines. regards, tom lane ---(end of broadcast)--- TIP 1: subscribe and unsubscribe commands go to [EMAIL PROTECTED]
