Hi,
Today, we encountered this serious memory issue with MonetDB.
*Data : *10 tables - each with ~600 columns - all tables are EMPTY (No rows).
*Query : *One query that involves with 25 joins across all the 10 tables.
*MonetDB version :* July2015-SP3
The above query is ran on the same MonetDB version with the same table structure with all tables empty on two different machines as follows.
*Scenario 1 - Query ran on Macbook Pro *
- RAM - 8 GB (with other processes like Chrome/Eclipse running in parallel) - Free disk space - ~100 GB - MonetDB July2015-SP3 downloaded as installable
The query is ran. *Expected result* - return an empty set in a few seconds. *Actual result* - returns an empty set in ~5 minutes RAM - 8 GB utilised completely. Swap space used from disk - 10 GB This swap space is cleared after sometime automatically (around 5 mins)
*Scenario 2 - With a CentOS virtual machine*
- RAM - 128 GB - Free disk space - ~650 GB - MonetDB July2015-SP3 compiled from source code
The query is ran. *Expected result* - return an empty set in a few seconds. *Actual result* - the query rebooted this high end CentOS machine. RAM - 128 GB utilised completely. After reboot, the swap memory was freed.
I am puzzled with the following questions.
1. Why should a query that runs on 10 EMPTY tables require memory in GBs? 2. How did this query manage to run on a Mac with just 8 GB RAM, but crashed a machine with 128 GB RAM?
Is this a known memory leak issue?
Any help much appreciated. Thanks in advance.
Regards, Vijay.