High DB load from SELECT on oc_cards due to lack of indexes

[tomneedham]

Multiple queries as follows:

SELECT `id`, `uri`, `lastmodified`, `etag`, `size`, `carddata` FROM `oc_cards` WHERE (`addressbookid` = '380') AND (`uri` = 'LDAP:foo@bar.vcf') LIMIT 1;

generates high db load during searching for cards as we don't have any indexes.

CREATE INDEX addressbookid_uri_index on oc_cards ( addressbookid, uri );

was observed to cut database load in half in production.

Creating a PR...

[butonic]

118200 entries in the table. no index ... 😞