metaSpout过大数据不准确

@killme2008
我们一个分析日志的应用，会统计日志里面的某个字段的出现次数，最后将结果存入数据库。数据分区开了10个。
1、在设置metaSpout的时候设置了48个。测试数据发送了100条，结果数据比实际数据多出一部分，多次测试，数据不一样但都不准确
2、其他不变条件不变，减少metaSpout的数量（测试了10，11），结果准确。

Start by reproducing the log-counting case with 10, 11, and 48 metaSpout instances against 10 data partitions, using the 100-message test described in the issue. Trace the counting and database-write path to identify why larger metaSpout counts produce varying totals; done means repeated runs match the 100-message input exactly.

Written by the indexing model from the issue text.