[MonetDB-users] Concurrent user threads
Hi, I read in the SQL Reference Manual that "The number of concurrent user threads is a configuration parameter.", but no information on the name or location or how to change it. Nor is there any info on what the default might be. I tried running multiple users and noticed that the performance degradation increased dramatically as the load increased. I looked at the Server and SQL manuals without luck. Thanks, Tah
Vashti_Ragoonath@ibi.com wrote:
Hi,
Hi thank you for using MonetDB.
I read in the SQL Reference Manual that “The number of concurrent user threads is a configuration parameter.”, but no information on the name or location or how to change it. Nor is there any info on what the default might be.
Indeed, the maximum number of concurrent users is hardwired into the code (currently 64). Any concurrent use leads to a fight for the resources. This means that most (commercial) systems allow large number of users but limit the admission of queries for execution (effective parallelism). It could indeed lead to superlinear degradation of performance, as any resource limited system would show.
I tried running multiple users and noticed that the performance degradation increased dramatically as the load increased. I looked at the Server and SQL manuals without luck.
To understand the impact of your application, you should study its behavior, e.g TRACE SELECT...., to see what queries are causing the problem. regards,Martin
Thanks,
Tah
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Hi Martin, Thanks so much for the reply. With respect to Part II of the question about performance degradation: 1. I was running the same query (Q1 from TPH-C) so nothing was wrong with it. 2. Single user - came back in a bit over 2 seconds 3. More than 1 user, from either JDBC or ODBC client, appears that the requests (all users running same Q1) were being processed serially. So for example, avg response times for: 1 user - 2.3 secs 3 users - 5.6 secs 5 users - 8.9 secs I enabled our traces and saw we were just waiting for a response from MonetDB when we had more than 1 user. I looked in the MonetDB manuals to see if I could debug it - not sure how to. How can I see what MonetDB is doing when it receives conncurrent user requests? Thanks tah1 wrote:
Hi,
I read in the SQL Reference Manual that "The number of concurrent user threads is a configuration parameter.", but no information on the name or location or how to change it. Nor is there any info on what the default might be. I tried running multiple users and noticed that the performance degradation increased dramatically as the load increased. I looked at the Server and SQL manuals without luck.
Thanks, Tah
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tah1 wrote:
Hi Martin,
Thanks so much for the reply. With respect to Part II of the question about performance degradation:
1. I was running the same query (Q1 from TPH-C) so nothing was wrong with it. 2. Single user - came back in a bit over 2 seconds 3. More than 1 user, from either JDBC or ODBC client, appears that the requests (all users running same Q1) were being processed serially. So for example, avg response times for: 1 user - 2.3 secs 3 users - 5.6 secs 5 users - 8.9 secs This it not unexpected. If you start N queries, then N query plans are taken into execution in parallel. Consider it like eating with N people from the same kettle. Standard computerscience analysis will show your this behavior.
I enabled our traces and saw we were just waiting for a response from MonetDB when we had more than 1 user. I looked in the MonetDB manuals to see MonetDB materializes the complete answer before returning to the user.
if I could debug it - not sure how to.
How can I see what MonetDB is doing when it receives conncurrent user requests? You can see what happens in the interpreter using the stethoscope. regards, Martin
Thanks
tah1 wrote:
Hi,
I read in the SQL Reference Manual that "The number of concurrent user threads is a configuration parameter.", but no information on the name or location or how to change it. Nor is there any info on what the default might be. I tried running multiple users and noticed that the performance degradation increased dramatically as the load increased. I looked at the Server and SQL manuals without luck.
Thanks, Tah
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participants (3)
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Martin Kersten -
tah1 -
Vashti_Ragoonath＠ibi.com