A simple benchmark was run on 2015-11-24 to measure the effectiveness of adding an index on pending_notify
$ sudo ./runner
Creating DB and table
Populating non-pending rows
Populating pending rows
+-----------+
| COUNT(id) |
+-----------+
| 5000 |
+-----------+
+-----------+
| COUNT(id) |
+-----------+
| 200000 |
+-----------+
Without any index
+----+-------------+-------+------+---------------+------+---------+------+--------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+--------+-----------------------------+
| 1 | SIMPLE | zones | ALL | NULL | NULL | NULL | NULL | 204013 | Using where; Using filesort |
+----+-------------+-------+------+---------------+------+---------+------+--------+-----------------------------+
Benchmark
Average number of seconds to run all queries: 0.137 seconds
Minimum number of seconds to run all queries: 0.122 seconds
Maximum number of seconds to run all queries: 0.158 seconds
Number of clients running queries: 3
Average number of queries per client: 1
With pending_notify index
+----+-------------+-------+------+--------------------+--------------------+---------+-------+------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+--------------------+--------------------+---------+-------+------+-----------------------------+
| 1 | SIMPLE | zones | ref | pending_notify_idx | pending_notify_idx | 2 | const | 4999 | Using where; Using filesort |
+----+-------------+-------+------+--------------------+--------------------+---------+-------+------+-----------------------------+
Benchmark
Average number of seconds to run all queries: 0.012 seconds
Minimum number of seconds to run all queries: 0.010 seconds
Maximum number of seconds to run all queries: 0.019 seconds
Number of clients running queries: 3
Average number of queries per client: 1
With created_at and pending_notify index
+----+-------------+-------+------+--------------------+--------------------+---------+-------+------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+--------------------+--------------------+---------+-------+------+-----------------------------+
| 1 | SIMPLE | zones | ref | pending_notify_idx | pending_notify_idx | 2 | const | 4999 | Using where; Using filesort |
+----+-------------+-------+------+--------------------+--------------------+---------+-------+------+-----------------------------+
Benchmark
Average number of seconds to run all queries: 0.012 seconds
Minimum number of seconds to run all queries: 0.010 seconds
Maximum number of seconds to run all queries: 0.018 seconds
Number of clients running queries: 3
Average number of queries per client: 1
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