Re: Adding LIMIT changes PostgreSQL plan from good to a bad one

[Michael Lewis]

I try to avoid DISTINCT and use GROUP BY when feasible, as well as avoiding
OR condition. If you combined anon1 and anon2 with UNION ALL, and did
(inner) join instead of left, or even moved all of that to EXISTS, perhaps
that gives you better consistent performance. Something like this-


SELECT contacts.id
FROM contacts
    JOIN contacts__aggregated AS contacts__aggregated_1 ON
         contacts__aggregated_1.company_id = contacts.company_id
         AND contacts__aggregated_1.contact_id = contacts.id
         AND contacts__aggregated_1.field_name = 'names'
WHERE contacts.company_id = '\x4c2118ad54397f271b000000'

AND EXISTS (
         SELECT
                     FROM contacts_values
                     WHERE contacts_values.field_id =
'\x000000000000000000000000'
                       AND contacts_values.field_name = 'facebook'
                       AND
nimble_contact_value_normalize(nimble_skip_long_values(contacts_values.value))
= nimble_contact_value_normalize('http://www.facebook.com/jon.ferrara'))
                       AND contacts_values.company_id = contacts.company_id
AND contacts_values.id = contacts.id
         UNION ALL
         SELECT
                     FROM contacts_values
                     WHERE contacts_values.field_id =
'\x000000000000000000000000'
                       AND contacts_values.field_name = 'last_name'
                       AND
nimble_contact_value_normalize(nimble_skip_long_values(contacts_values.value))
= nimble_contact_value_normalize('Ferrara')
                       AND contacts_values.company_id = contacts.company_id
AND contacts_values.id = contacts.id
)

ORDER BY contacts__aggregated_1.value ASC
LIMIT 30 OFFSET 0;