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<chapter id="performance-tips">

<title>Performance Tips</title>

For example, we might do:

<screen>

SELECT attname, n_distinct, most_common_vals

SELECT attname, inherited, n_distinct,

array_to_string(most_common_vals, E'\n') as most_common_vals

FROM pg_stats

WHERE tablename = 'road';

attname | n_distinct | most_common_vals

---------+------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

name | -0.467008 | {"I- 580 Ramp","I- 880 Ramp","Sp Railroad ","I- 580 ","I- 680 Ramp","I- 80 Ramp","14th St ","5th St ","Mission Blvd","I- 880 "}

thepath | 20 | {"[(-122.089,37.71),(-122.0886,37.711)]"}

attname | inherited | n_distinct | most_common_vals

---------+-----------+------------+------------------------------------

name | f | -0.363388 | I- 580 Ramp+

| | | I- 880 Ramp+

| | | Sp Railroad +

| | | I- 580 +

| | | I- 680 Ramp

name | t | -0.284859 | I- 880 Ramp+

| | | I- 580 Ramp+

| | | I- 680 Ramp+

| | | I- 580 +

| | | State Hwy 13 Ramp

(2 rows)

</screen>

Note that two rows are displayed for the same column, one corresponding

to the complete inheritance hierarchy starting at the

<literal>road</literal> table (<literal>inherited</>=<literal>t</>),

and another one including only the <literal>road</literal> table itself

(<literal>inherited</>=<literal>f</>).

</para>

<para>