Refactor how heap_prune_chain() updates prunable_xid

In preparation of freezing and counting tuples which are not
candidates for pruning, split heap_prune_record_unchanged() into
multiple functions, depending the kind of line pointer. That's not too
interesting right now, but makes the next commit smaller.

Recording the lowest soon-to-be prunable xid is one of the actions we
take for unchanged LP_NORMAL item pointers but not for others, so move
that to the new heap_prune_record_unchanged_lp_normal() function. The
next commit will add more actions to these functions.

Author: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://www.postgresql.org/message-id/20240330055710.kqg6ii2cdojsxgje@liskov

diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c
index ef563e19aa59daf08ffb5271d93f82f9123a4dbe..1b5bf990d210375f63a85b6bd91f7465efb5884e 100644 (file)
--- a/src/backend/access/heap/pruneheap.c
+++ b/src/backend/access/heap/pruneheap.c
@@ -78,7 +78,11 @@ static void heap_prune_record_redirect(PruneState *prstate,
 static void heap_prune_record_dead(PruneState *prstate, OffsetNumber offnum, bool was_normal);
 static void heap_prune_record_dead_or_unused(PruneState *prstate, OffsetNumber offnum, bool was_normal);
 static void heap_prune_record_unused(PruneState *prstate, OffsetNumber offnum, bool was_normal);
-static void heap_prune_record_unchanged(PruneState *prstate, OffsetNumber offnum);
+
+static void heap_prune_record_unchanged_lp_unused(Page page, PruneState *prstate, OffsetNumber offnum);
+static void heap_prune_record_unchanged_lp_normal(Page page, int8 *htsv, PruneState *prstate, OffsetNumber offnum);
+static void heap_prune_record_unchanged_lp_dead(Page page, PruneState *prstate, OffsetNumber offnum);
+static void heap_prune_record_unchanged_lp_redirect(PruneState *prstate, OffsetNumber offnum);
 
 static void page_verify_redirects(Page page);
 
@@ -311,7 +315,7 @@ heap_page_prune(Relation relation, Buffer buffer,
        /* Nothing to do if slot doesn't contain a tuple */
        if (!ItemIdIsUsed(itemid))
        {
-           heap_prune_record_unchanged(&prstate, offnum);
+           heap_prune_record_unchanged_lp_unused(page, &prstate, offnum);
            continue;
        }
 
@@ -324,7 +328,7 @@ heap_page_prune(Relation relation, Buffer buffer,
            if (unlikely(prstate.mark_unused_now))
                heap_prune_record_unused(&prstate, offnum, false);
            else
-               heap_prune_record_unchanged(&prstate, offnum);
+               heap_prune_record_unchanged_lp_dead(page, &prstate, offnum);
            continue;
        }
 
@@ -434,7 +438,7 @@ heap_page_prune(Relation relation, Buffer buffer,
            }
        }
        else
-           heap_prune_record_unchanged(&prstate, offnum);
+           heap_prune_record_unchanged_lp_normal(page, presult->htsv, &prstate, offnum);
    }
 
    /* We should now have processed every tuple exactly once  */
@@ -652,9 +656,6 @@ heap_prune_chain(Page page, BlockNumber blockno, OffsetNumber maxoff,
         */
        chainitems[nchain++] = offnum;
 
-       /*
-        * Check tuple's visibility status.
-        */
        switch (htsv_get_valid_status(htsv[offnum]))
        {
            case HEAPTUPLE_DEAD:
@@ -670,9 +671,6 @@ heap_prune_chain(Page page, BlockNumber blockno, OffsetNumber maxoff,
            case HEAPTUPLE_RECENTLY_DEAD:
 
                /*
-                * This tuple may soon become DEAD.  Update the hint field so
-                * that the page is reconsidered for pruning in future.
-                *
                 * We don't need to advance the conflict horizon for
                 * RECENTLY_DEAD tuples, even if we are removing them.  This
                 * is because we only remove RECENTLY_DEAD tuples if they
@@ -681,8 +679,6 @@ heap_prune_chain(Page page, BlockNumber blockno, OffsetNumber maxoff,
                 * tuple by virtue of being later in the chain.  We will have
                 * advanced the conflict horizon for the DEAD tuple.
                 */
-               heap_prune_record_prunable(prstate,
-                                          HeapTupleHeaderGetUpdateXid(htup));
 
                /*
                 * Advance past RECENTLY_DEAD tuples just in case there's a
@@ -693,24 +689,8 @@ heap_prune_chain(Page page, BlockNumber blockno, OffsetNumber maxoff,
                break;
 
            case HEAPTUPLE_DELETE_IN_PROGRESS:
-
-               /*
-                * This tuple may soon become DEAD.  Update the hint field so
-                * that the page is reconsidered for pruning in future.
-                */
-               heap_prune_record_prunable(prstate,
-                                          HeapTupleHeaderGetUpdateXid(htup));
-               goto process_chain;
-
            case HEAPTUPLE_LIVE:
            case HEAPTUPLE_INSERT_IN_PROGRESS:
-
-               /*
-                * If we wanted to optimize for aborts, we might consider
-                * marking the page prunable when we see INSERT_IN_PROGRESS.
-                * But we don't.  See related decisions about when to mark the
-                * page prunable in heapam.c.
-                */
                goto process_chain;
 
            default:
@@ -757,8 +737,15 @@ process_chain:
         * No DEAD tuple was found, so the chain is entirely composed of
         * normal, unchanged tuples.  Leave it alone.
         */
-       for (int i = 0; i < nchain; i++)
-           heap_prune_record_unchanged(prstate, chainitems[i]);
+       int         i = 0;
+
+       if (ItemIdIsRedirected(rootlp))
+       {
+           heap_prune_record_unchanged_lp_redirect(prstate, rootoffnum);
+           i++;
+       }
+       for (; i < nchain; i++)
+           heap_prune_record_unchanged_lp_normal(page, htsv, prstate, chainitems[i]);
    }
    else if (ndeadchain == nchain)
    {
@@ -784,7 +771,7 @@ process_chain:
 
        /* the rest of tuples in the chain are normal, unchanged tuples */
        for (int i = ndeadchain; i < nchain; i++)
-           heap_prune_record_unchanged(prstate, chainitems[i]);
+           heap_prune_record_unchanged_lp_normal(page, htsv, prstate, chainitems[i]);
    }
 }
 
@@ -894,9 +881,81 @@ heap_prune_record_unused(PruneState *prstate, OffsetNumber offnum, bool was_norm
        prstate->ndeleted++;
 }
 
-/* Record a line pointer that is left unchanged */
+/*
+ * Record an unused line pointer that is left unchanged.
+ */
+static void
+heap_prune_record_unchanged_lp_unused(Page page, PruneState *prstate, OffsetNumber offnum)
+{
+   Assert(!prstate->processed[offnum]);
+   prstate->processed[offnum] = true;
+}
+
+/*
+ * Record LP_NORMAL line pointer that is left unchanged.
+ */
+static void
+heap_prune_record_unchanged_lp_normal(Page page, int8 *htsv, PruneState *prstate, OffsetNumber offnum)
+{
+   HeapTupleHeader htup;
+
+   Assert(!prstate->processed[offnum]);
+   prstate->processed[offnum] = true;
+
+   switch (htsv[offnum])
+   {
+       case HEAPTUPLE_LIVE:
+       case HEAPTUPLE_INSERT_IN_PROGRESS:
+
+           /*
+            * If we wanted to optimize for aborts, we might consider marking
+            * the page prunable when we see INSERT_IN_PROGRESS.  But we
+            * don't.  See related decisions about when to mark the page
+            * prunable in heapam.c.
+            */
+           break;
+
+       case HEAPTUPLE_RECENTLY_DEAD:
+       case HEAPTUPLE_DELETE_IN_PROGRESS:
+
+           htup = (HeapTupleHeader) PageGetItem(page, PageGetItemId(page, offnum));
+
+           /*
+            * This tuple may soon become DEAD.  Update the hint field so that
+            * the page is reconsidered for pruning in future.
+            */
+           heap_prune_record_prunable(prstate,
+                                      HeapTupleHeaderGetUpdateXid(htup));
+           break;
+
+
+       default:
+
+           /*
+            * DEAD tuples should've been passed to heap_prune_record_dead()
+            * or heap_prune_record_unused() instead.
+            */
+           elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result %d", htsv[offnum]);
+           break;
+   }
+}
+
+
+/*
+ * Record line pointer that was already LP_DEAD and is left unchanged.
+ */
+static void
+heap_prune_record_unchanged_lp_dead(Page page, PruneState *prstate, OffsetNumber offnum)
+{
+   Assert(!prstate->processed[offnum]);
+   prstate->processed[offnum] = true;
+}
+
+/*
+ * Record LP_REDIRECT that is left unchanged.
+ */
 static void
-heap_prune_record_unchanged(PruneState *prstate, OffsetNumber offnum)
+heap_prune_record_unchanged_lp_redirect(PruneState *prstate, OffsetNumber offnum)
 {
    Assert(!prstate->processed[offnum]);
    prstate->processed[offnum] = true;