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Avoid looping through line pointers twice in PageRepairFragmentation().

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There doesn't seem to be any good reason to do the filling of the
itemidbase[] array separately from the first traversal of the pointers.
It's certainly not a win if there are any line pointers with storage,
and even if there aren't, this change doesn't insert code into the part
of the first loop that will be traversed in that case.  So let's just
merge the two loops.

Yura Sokolov, reviewed by Claudio Freire

Discussion: https://postgr.es/m/e49befcc6f1d7099834c6fdf5c675a60@postgrespro.ru
This commit is contained in:
Tom Lane 2017-11-03 17:21:59 -04:00
parent 4c11d2c559
commit a9169f0200
1 changed files with 26 additions and 30 deletions
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56
src/backend/storage/page/bufpage.c
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@ -481,6 +481,8 @@ PageRepairFragmentation(Page page)
Offset pd_lower = ((PageHeader) page)->pd_lower;
Offset pd_upper = ((PageHeader) page)->pd_upper;
Offset pd_special = ((PageHeader) page)->pd_special;
itemIdSortData itemidbase[MaxHeapTuplesPerPage];
itemIdSort itemidptr;
ItemId lp;
int nline,
nstorage,
@ -505,45 +507,23 @@ PageRepairFragmentation(Page page)
errmsg("corrupted page pointers: lower = %u, upper = %u, special = %u",
pd_lower, pd_upper, pd_special)));
/*
* Run through the line pointer array and collect data about live items.
*/
nline = PageGetMaxOffsetNumber(page);
nunused = nstorage = 0;
itemidptr = itemidbase;
nunused = totallen = 0;
for (i = FirstOffsetNumber; i <= nline; i++)
{
lp = PageGetItemId(page, i);
if (ItemIdIsUsed(lp))
{
if (ItemIdHasStorage(lp))
nstorage++;
}
else
{
/* Unused entries should have lp_len = 0, but make sure */
ItemIdSetUnused(lp);
nunused++;
}
}
if (nstorage == 0)
{
/* Page is completely empty, so just reset it quickly */
((PageHeader) page)->pd_upper = pd_special;
}
else
{
/* Need to compact the page the hard way */
itemIdSortData itemidbase[MaxHeapTuplesPerPage];
itemIdSort itemidptr = itemidbase;
totallen = 0;
for (i = 0; i < nline; i++)
{
lp = PageGetItemId(page, i + 1);
if (ItemIdHasStorage(lp))
{
itemidptr->offsetindex = i;
itemidptr->offsetindex = i - 1;
itemidptr->itemoff = ItemIdGetOffset(lp);
if (itemidptr->itemoff < (int) pd_upper ||
itemidptr->itemoff >= (int) pd_special)
if (unlikely(itemidptr->itemoff < (int) pd_upper ||
itemidptr->itemoff >= (int) pd_special))
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
errmsg("corrupted item pointer: %u",
@ -553,7 +533,23 @@ PageRepairFragmentation(Page page)
itemidptr++;
}
}
else
{
/* Unused entries should have lp_len = 0, but make sure */
ItemIdSetUnused(lp);
nunused++;
}
}
nstorage = itemidptr - itemidbase;
if (nstorage == 0)
{
/* Page is completely empty, so just reset it quickly */
((PageHeader) page)->pd_upper = pd_special;
}
else
{
/* Need to compact the page the hard way */
if (totallen > (Size) (pd_special - pd_lower))
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),