diff options
Diffstat (limited to 'src/backend/commands/vacuum.c')
| -rw-r--r-- | src/backend/commands/vacuum.c | 30 |
1 files changed, 15 insertions, 15 deletions
diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index 224c34f6e7..5cbf3a04f8 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -459,7 +459,7 @@ vacuum_set_xid_limits(int freeze_min_age, * If we scanned the whole relation then we should just use the count of * live tuples seen; but if we did not, we should not trust the count * unreservedly, especially not in VACUUM, which may have scanned a quite - * nonrandom subset of the table. When we have only partial information, + * nonrandom subset of the table. When we have only partial information, * we take the old value of pg_class.reltuples as a measurement of the * tuple density in the unscanned pages. * @@ -471,7 +471,7 @@ vac_estimate_reltuples(Relation relation, bool is_analyze, BlockNumber scanned_pages, double scanned_tuples) { - BlockNumber old_rel_pages = relation->rd_rel->relpages; + BlockNumber old_rel_pages = relation->rd_rel->relpages; double old_rel_tuples = relation->rd_rel->reltuples; double old_density; double new_density; @@ -483,8 +483,8 @@ vac_estimate_reltuples(Relation relation, bool is_analyze, return scanned_tuples; /* - * If scanned_pages is zero but total_pages isn't, keep the existing - * value of reltuples. + * If scanned_pages is zero but total_pages isn't, keep the existing value + * of reltuples. */ if (scanned_pages == 0) return old_rel_tuples; @@ -498,23 +498,23 @@ vac_estimate_reltuples(Relation relation, bool is_analyze, /* * Okay, we've covered the corner cases. The normal calculation is to - * convert the old measurement to a density (tuples per page), then - * update the density using an exponential-moving-average approach, - * and finally compute reltuples as updated_density * total_pages. + * convert the old measurement to a density (tuples per page), then update + * the density using an exponential-moving-average approach, and finally + * compute reltuples as updated_density * total_pages. * - * For ANALYZE, the moving average multiplier is just the fraction of - * the table's pages we scanned. This is equivalent to assuming - * that the tuple density in the unscanned pages didn't change. Of - * course, it probably did, if the new density measurement is different. - * But over repeated cycles, the value of reltuples will converge towards - * the correct value, if repeated measurements show the same new density. + * For ANALYZE, the moving average multiplier is just the fraction of the + * table's pages we scanned. This is equivalent to assuming that the + * tuple density in the unscanned pages didn't change. Of course, it + * probably did, if the new density measurement is different. But over + * repeated cycles, the value of reltuples will converge towards the + * correct value, if repeated measurements show the same new density. * * For VACUUM, the situation is a bit different: we have looked at a * nonrandom sample of pages, but we know for certain that the pages we * didn't look at are precisely the ones that haven't changed lately. * Thus, there is a reasonable argument for doing exactly the same thing - * as for the ANALYZE case, that is use the old density measurement as - * the value for the unscanned pages. + * as for the ANALYZE case, that is use the old density measurement as the + * value for the unscanned pages. * * This logic could probably use further refinement. */ |