Hi
Simply because MonetDB will already use all cores whenever it can.
This means less inter-process communication and less contention
for resources.
Furthermore, there might be decisions being taken due to lack
of knowledge about the partitions, which should be set using
the ANALYZE command.
regards, Martin
On 19/03/2017 04:25, Manish gupta wrote:
______________________________Dear all,
I am checking the performance of merge table vs single table on single machine with 4 cores. The fact table contains ~10million records. I am using # MonetDB 5 server v11.25.9 "Dec2016-SP2" on windows machine ( core i7 16GB physical ram ).
I have created a merge table which contains fact table and 3 blank copies of fact table. I am seeing surprisingly slow performance of merge table queries compared to base table queries.
Base table query
=================
sql>select sum(f_1_1_1), count(*), f_1_1_7,f_1_1_5 from t3760_279_1_1 group by f_1_1_7,f_1_1_5 order by sum(f_1_1_1) desc limit 10;
+-----------+------+---------+---------+
| L2 | L5 | f_1_1_7 | f_1_1_5 |
+===========+======+=========+=========+
| 125885351 | 14 | SALE | 8084869 |
| 125629268 | 15 | SALE | 6852518 |
| 121733416 | 16 | SALE | 5440605 |
| 110328868 | 13 | SALE | 4842411 |
| 100848236 | 11 | SALE | 8068509 |
| 100719291 | 16 | SALE | 5822736 |
| 93127875 | 11 | SALE | 6529612 |
| 91034094 | 13 | SALE | 3401293 |
| 90766181 | 10 | SALE | 8084900 |
| 88848574 | 10 | SALE | 2660811 |
+-----------+------+---------+---------+
10 tuples (44.2s)
Merge Table Query
=================
sql>select sum(f_1_1_1), count(*), f_1_1_7,f_1_1_5 from mt279_1_1 group by f_1_1_7,f_1_1_5 order by sum(f_1_1_1) desc limit 10;
+-----------+------+---------+---------+
| L2 | L5 | f_1_1_7 | f_1_1_5 |
+===========+======+=========+=========+
| 125885351 | 14 | SALE | 8084869 |
| 125629268 | 15 | SALE | 6852518 |
| 121733416 | 16 | SALE | 5440605 |
| 110328868 | 13 | SALE | 4842411 |
| 100848236 | 11 | SALE | 8068509 |
| 100719291 | 16 | SALE | 5822736 |
| 93127875 | 11 | SALE | 6529612 |
| 91034094 | 13 | SALE | 3401293 |
| 90766181 | 10 | SALE | 8084900 |
| 88848574 | 10 | SALE | 2660811 |
+-----------+------+---------+---------+
10 tuples (1m 51s)
For the same results ( because merge table is containing the base table and 3 blank copies of base table ), merge table query is taking more than 2.5 times the base table runtime. Why is it so?
Thanks,
Mohit
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