i'm doing a performance audit and noticed something odd.
we tested a table a while back, by creating lots of indexes that match
different queries (30+).
for simplicity, here's a two column table:
CREATE TABLE foo (id INT PRIMARY KEY
value INT NOT NULL DEFAULT 0,
);
The indexes were generated by a script, so we had things like:
CREATE INDEX idx_test_foo_id_asc ON foo(id ASC);
CREATE INDEX idx_test_foo_id_desc ON foo(id DESC);
CREATE INDEX idx_test_foo_val_asc ON foo(value ASC);
CREATE INDEX idx_test_foo_value_desc ON foo(value DESC);
What I noticed when checking stats earlier, is that although
`idx_test_foo_id_asc` is the same as the PKEY... it was used about 10x more
than the pkey.
Does anyone know of this is just random (perhaps due to the name being sorted
earlier) or there is some other reason that index would be selected ?
my concern in deleting it, is that it might be preferred for queries due to
hinting from the explicit 'order by' (even though the contents are the same)
and I may lose an index being leveraged in that query.
It's on a GIANT table, so it would be hard to recreate.
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