vacuumlazy.c: Standardize rel_pages terminology.

VACUUM's rel_pages field indicates the size of the target heap rel just
after the table_relation_vacuum() operation began.  There are specific
expectations around how rel_pages can be related to other nearby state.
In particular, the range of rel_pages must contain every tuple in the
relation whose tuple headers might contain an XID < OldestXmin.

Consistently refer to the field as rel_pages to make this clearer and
more discoverable.

This is follow-up work to commit 73f6ec3d from earlier today.

Author: Peter Geoghegan <pg@bowt.ie>
Reviewed-By: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20220311031351.sbge5m2bpvy2ttxg@alap3.anarazel.de

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 7982139baa8bd9f1ef06bbdf48b3338763724f4c..620b7a7af5bd6c0b8c7e335e07581b196ba26dd8 100644 (file)
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -825,7 +825,7 @@ static void
 lazy_scan_heap(LVRelState *vacrel, int nworkers)
 {
        VacDeadItems *dead_items;
-       BlockNumber nblocks = vacrel->rel_pages,
+       BlockNumber rel_pages = vacrel->rel_pages,
                                blkno,
                                next_unskippable_block,
                                next_failsafe_block,
@@ -858,7 +858,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
 
        /* Report that we're scanning the heap, advertising total # of blocks */
        initprog_val[0] = PROGRESS_VACUUM_PHASE_SCAN_HEAP;
-       initprog_val[1] = nblocks;
+       initprog_val[1] = rel_pages;
        initprog_val[2] = dead_items->max_items;
        pgstat_progress_update_multi_param(3, initprog_index, initprog_val);
 
@@ -882,9 +882,9 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
         * Before entering the main loop, establish the invariant that
         * next_unskippable_block is the next block number >= blkno that we can't
         * skip based on the visibility map, either all-visible for a regular scan
-        * or all-frozen for an aggressive scan.  We set it to nblocks if there's
-        * no such block.  We also set up the skipping_blocks flag correctly at
-        * this stage.
+        * or all-frozen for an aggressive scan.  We set it to rel_pages when
+        * there's no such block.  We also set up the skipping_blocks flag
+        * correctly at this stage.
         *
         * Note: The value returned by visibilitymap_get_status could be slightly
         * out-of-date, since we make this test before reading the corresponding
@@ -902,7 +902,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
        next_unskippable_block = 0;
        if (vacrel->skipwithvm)
        {
-               while (next_unskippable_block < nblocks)
+               while (next_unskippable_block < rel_pages)
                {
                        uint8           vmstatus;
 
@@ -929,7 +929,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
        else
                skipping_blocks = false;
 
-       for (blkno = 0; blkno < nblocks; blkno++)
+       for (blkno = 0; blkno < rel_pages; blkno++)
        {
                Buffer          buf;
                Page            page;
@@ -947,7 +947,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
                        next_unskippable_block++;
                        if (vacrel->skipwithvm)
                        {
-                               while (next_unskippable_block < nblocks)
+                               while (next_unskippable_block < rel_pages)
                                {
                                        uint8           vmskipflags;
 
@@ -992,7 +992,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
                        /*
                         * The current page can be skipped if we've seen a long enough run
                         * of skippable blocks to justify skipping it -- provided it's not
-                        * the last page in the relation (according to rel_pages/nblocks).
+                        * the last page in the relation (according to rel_pages).
                         *
                         * We always scan the table's last page to determine whether it
                         * has tuples or not, even if it would otherwise be skipped. This
@@ -1000,7 +1000,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
                         * on the table to attempt a truncation that just fails
                         * immediately because there are tuples on the last page.
                         */
-                       if (skipping_blocks && blkno < nblocks - 1)
+                       if (skipping_blocks && blkno < rel_pages - 1)
                        {
                                /*
                                 * Tricky, tricky.  If this is in aggressive vacuum, the page
@@ -1367,7 +1367,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
        vacrel->blkno = InvalidBlockNumber;
 
        /* now we can compute the new value for pg_class.reltuples */
-       vacrel->new_live_tuples = vac_estimate_reltuples(vacrel->rel, nblocks,
+       vacrel->new_live_tuples = vac_estimate_reltuples(vacrel->rel, rel_pages,
                                                                                                         vacrel->scanned_pages,
                                                                                                         vacrel->live_tuples);