From f0381680fa480a8794d00566cef21178cd63d74e Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 11 Jan 2014 13:41:41 -0500
Subject: [PATCH] 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 9612a276f35..4fdb67d1b37 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -2727,7 +2727,21 @@ 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;
--
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