Hi everyone,
I found the solution and it has nothing to do with my ramblings above.
It turns out that when I do (.executeQuery stmt), the MySQL JDBC
driver fetches the entire resultset from the server at once.
Here is how to make it lazy also on the JDBC side:
(let [conn (datasource/connection datasource/cdr-c4)
stmt (.prepareStatement
conn
(format "SELECT
SUBSTRING(a,5) AS a,
SUBSTRING(b,3) AS b,
SUBSTRING(st,1,14) AS st,
duration/1000 AS duration
FROM `call`
WHERE st LIKE '%s%%'
ORDER BY st" st-prefix)
java.sql.ResultSet/TYPE_FORWARD_ONLY
java.sql.ResultSet/CONCUR_READ_ONLY)]
(.setFetchSize stmt Integer/MIN_VALUE)
...
With this change, everything works as expected.
Details about why this works:
http://dev.mysql.com/doc/refman/5.0/en/connector-j-reference-implementation-notes.html
(scroll down to the section on "ResultSet")
(Note, that this is a MySQL-only solution, other JDBC drivers may
require different tricks.)
P.s. I still don't understand though why the 'calls' argument to the
store-calls function is not a held reference to the head of the lazy
seq...
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