postgres.git / summary / log / commit / refs

commit    00b77771aa61c688fbca41fdb4657381b3a2fc90
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Sat Jan 11 18:41:41 2014 +0000
First released in: 9.4.0, 8.4.20, 9.0.16, 9.1.12, 9.2.7, 9.3.3

    Fix compute_scalar_stats() for case that all values exceed WIDTH_THRESHOLD.
    
    The standard typanalyze functions skip over values whose detoasted size
    exceeds WIDTH_THRESHOLD (1024 bytes), so as to limit memory bloat during
    ANALYZE.  However, we (I think I, actually :-() failed to consider the
    possibility that *every* non-null value in a column is too wide.  While
    compute_minimal_stats() seems to behave reasonably anyway in such a case,
    compute_scalar_stats() just fell through and generated no pg_statistic
    entry at all.  That's unnecessarily pessimistic: we can still produce
    valid stanullfrac and stawidth values in such cases, since we do include
    too-wide values in the average-width calculation.  Furthermore, since the
    general assumption in this code is that too-wide values are probably all
    distinct from each other, it seems reasonable to set stadistinct to -1
    ("all distinct").
    
    Per complaint from Kadri Raudsepp.  This has been like this since roughly
    neolithic times, so back-patch to all supported branches.


 src/backend/commands/analyze.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 7ac40cb404d..2bb1fd791f5 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -2392,7 +2392,21 @@ compute_scalar_stats(VacAttrStatsP stats,
 			slot_idx++;
 		}
 	}
-	else if (nonnull_cnt == 0 && null_cnt > 0)
+	else if (nonnull_cnt > 0)
+	{
+		/* We found some non-null values, but they were all too wide */
+		Assert(nonnull_cnt == toowide_cnt);
+		stats->stats_valid = true;
+		/* Do the simple null-frac and width stats */
+		stats->stanullfrac = (double) null_cnt / (double) samplerows;
+		if (is_varwidth)
+			stats->stawidth = total_width / (double) nonnull_cnt;
+		else
+			stats->stawidth = stats->attrtype->typlen;
+		/* Assume all too-wide values are distinct, so it's a unique column */
+		stats->stadistinct = -1.0;
+	}
+	else if (null_cnt > 0)
 	{
 		/* We found only nulls; assume the column is entirely null */
 		stats->stats_valid = true;


[parent: d68a65b0134a]