On 7.4 I get
select * from pg_stats where tablename = 'attribute' and attname = 'fknamestringid';
schemaname | tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation
------------+-----------+----------------+-----------+-----------+------------+-----------------------------------------------------+-------------------------------------------------------------------------------------+----------------------------------------------------------+-------------
common | attribute | fknamestringid | 0 | 4 | 124 | {2524,2434,2523,2599,2595,2592,2596,2528,2586,2446} | {0.132333,0.13,0.0766667,0.0373333,0.0366667,0.0333333,0.031,0.029,0.0263333,0.019} | {2433,2441,2455,2462,2473,2479,2484,2492,2505,2574,2598} | -0.22864
(1 row)
On 8
select * from pg_stats where tablename = 'attribute' and attname = 'fknamestringid';
schemaname | tablename | attname | null_frac | avg_width | n_distinct | most_common_vals | most_common_freqs | histogram_bounds | correlation
------------+-----------+----------------+-----------+-----------+------------+-----------------------------------------------------+-----------------------------------------------------------------------------------+----------------------------------------------------------+-------------
common | attribute | fknamestringid | 0 | 4 | 80 | {2524,2434,2530,2522,2525,2523,2527,2526,2574,2531} | {0.219333,0.199333,0.076,0.0643333,0.0616667,0.05,0.0453333,0.042,0.04,0.0286667} | {2437,2528,2529,2538,2539,2540,2554,2562,2575,2584,2637} | 0.0274016
Tom Lane wrote:
I was able to duplicate this behavior with dummy data that had only a few distinct values for fknamestringid --- the planner then thinks that the index probe into attribute will match a lot of rows and hence take a long time. Could we see your pg_stats row for fknamestringid, ie
select * from pg_stats where tablename = 'attribute' and attname = 'fknamestringid';
It would be interesting to see the same for your 7.4 installation too.
regards, tom lane
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