Changes improve the performance of INSERT and UPDATE

Hi all,

This small patch improves the performance of INSERT and UPDATE.  By my
machine, these changes raised the performance about 5%~10% in pgbench.
Please take a benchmark in a reliable environment.  Since I may forget
some required changes, I specify that this patch is experimental.  But
note that all regression tests have passed.

Thanks,

--
Hiroki Kataoka <kataoka@interwiz.jp>
diff -ru postgresql-cvs.orig/src/backend/storage/page/bufpage.c postgresql-cvs/src/backend/storage/page/bufpage.c
--- postgresql-cvs.orig/src/backend/storage/page/bufpage.c    2005-06-15 16:53:00.000000000 +0900
+++ postgresql-cvs/src/backend/storage/page/bufpage.c    2005-07-14 07:41:11.000000000 +0900
@@ -42,6 +42,7 @@
     p->pd_lower = SizeOfPageHeaderData;
     p->pd_upper = pageSize - specialSize;
     p->pd_special = pageSize - specialSize;
+    p->pd_insoff = FirstOffsetNumber;
     PageSetPageSizeAndVersion(page, pageSize, PG_PAGE_LAYOUT_VERSION);
 }

@@ -100,7 +101,7 @@
  *    If offsetNumber is valid and <= current max offset in the page,
  *    insert item into the array at that position by shuffling ItemId's
  *    down to make room.
- *    If offsetNumber is not valid, then assign one by finding the first
+ *    If offsetNumber is not valid, then assign one by finding the next
  *    one that is both unused and deallocated.
  *
  *    !!! EREPORT(ERROR) IS DISALLOWED HERE !!!
@@ -120,6 +121,7 @@
     OffsetNumber limit;
     bool        needshuffle = false;
     bool        overwritemode = (flags & OverwritePageMode) != 0;
+    bool        findunusedlinp = false;

     flags &= ~OverwritePageMode;

@@ -165,9 +167,15 @@
     }
     else
     {
-        /* offsetNumber was not passed in, so find a free slot */
-        /* look for "recyclable" (unused & deallocated) ItemId */
-        for (offsetNumber = 1; offsetNumber < limit; offsetNumber++)
+        /* offsetNumber was not passed in, try to use pd_insoff */
+        if (OffsetNumberIsValid(phdr->pd_insoff))
+            offsetNumber = phdr->pd_insoff;
+        else
+            offsetNumber = FirstOffsetNumber;
+
+        /* so find a free slot look for "recyclable" (unused & deallocated) */
+        /* ItemId */
+        for (; offsetNumber < limit; offsetNumber++)
         {
             itemId = PageGetItemId(phdr, offsetNumber);
             if (((itemId->lp_flags & LP_USED) == 0) &&
@@ -175,6 +183,8 @@
                 break;
         }
         /* if no free slot, we'll put it at limit (1st open slot) */
+
+        findunusedlinp = true;
     }

     if (offsetNumber > limit)
@@ -222,6 +232,8 @@
     /* adjust page header */
     phdr->pd_lower = (LocationIndex) lower;
     phdr->pd_upper = (LocationIndex) upper;
+    if (findunusedlinp)
+        phdr->pd_insoff = OffsetNumberNext(offsetNumber);

     return offsetNumber;
 }
@@ -345,8 +357,13 @@
             lp->lp_flags &= ~(LP_USED | LP_DELETE);
         if (lp->lp_flags & LP_USED)
             nused++;
-        else if (unused)
-            unused[i - nused] = (OffsetNumber) i;
+        else
+        {
+            if (i - nused == 0)    /* check if it's first unused line pointer */
+                ((PageHeader) page)->pd_insoff = (OffsetNumber) i + 1;
+            if (unused)
+                unused[i - nused] = (OffsetNumber) i;
+        }
     }

     if (nused == 0)
diff -ru postgresql-cvs.orig/src/include/storage/bufpage.h postgresql-cvs/src/include/storage/bufpage.h
--- postgresql-cvs.orig/src/include/storage/bufpage.h    2005-04-29 06:47:18.000000000 +0900
+++ postgresql-cvs/src/include/storage/bufpage.h    2005-07-14 06:57:03.000000000 +0900
@@ -125,6 +125,7 @@
     LocationIndex pd_lower;        /* offset to start of free space */
     LocationIndex pd_upper;        /* offset to end of free space */
     LocationIndex pd_special;    /* offset to start of special space */
+    OffsetNumber pd_insoff;        /* offset number for next new item */
     uint16        pd_pagesize_version;
     ItemIdData    pd_linp[1];        /* beginning of line pointer array */
 } PageHeaderData;