[ipaddr]

Just to make this fun.

Adding an index now increases the insert operation cost/time and adds additional storage.

If insert speed/volume is more important than reads keep the indexes away. Replicate and create an index on that copy.

[sigstoat]

> Adding an index now increases the insert operation cost/time

that insert is happening after you've checked the table to see if the record is present. so two operations whose times we care about are "select and accept email" and "select, tell the sender to come back in 20 minutes, and then insert".

the insert time effectively doesn't matter, unless you've decided to abandon discussion of the original table entirely without mentioning it.