Questions tagged [parallelism]

Reducing run times by breaking a problem into parts that can be completed by separate execution paths simultaneously.

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1answer
322 views

SQL Server parallelism issue

I am rather new to SQL Server administrations, I am running an SSIS that never ends... A) looking at the processes using SELECT r.*, t.text FROM sys.dm_exec_requests r CROSS APPLY sys....
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4answers
3k views

Dealing with CXPACKET waits - setting cost threshold for parallelism

As a follow-up to my previous question on perf troubleshooting a Sharepoint site, I was wondering if I could do something about the CXPACKET waits. I know the knee-jerk solution is to turn off all ...
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3answers
5k views

Parallel Statistics Update

In SQL Server 2008 or later, is UPDATE STATISTICS WITH FULLSCAN a single threaded operation or it can use parallelism? How about update statistics with default sampling - can it use parallelism? I don'...
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1answer
466 views

What is the “Data partitioned, Shared-Nothing, Parallel Database” solution for PostgreSQL ? [closed]

I was looking for a open source parallel database solution. It seems Postgres-XC is a viable solution. However, I don't need the replication. In this case, is there any better solution towards read ...
2
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2answers
3k views

Are problems with parallelism more common today? What issues can arise from parallelism?

This is a very general question so I don't give much specific information. I am more interested in parallelism and its possible drawbacks. Generally I am all for parallelism as something useful and ...
12
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3answers
28k views

Why is an aggregate query significantly faster with a GROUP BY clause than without one?

I'm just curious why an aggregate query runs so much faster with a GROUP BY clause than without one. For example, this query takes almost 10 seconds to run SELECT MIN(CreatedDate) FROM MyTable WHERE ...
10
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2answers
21k views

Using multiple cores for single MySQL queries on Debian

I am running a MySQL server for tests on a VM (VMWare) with Debian as guest OS. The guest has four emulated CPU cores, so I set thread_concurrency to four. I am doing expensive joins on large tables, ...
2
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1answer
8k views

In Oracle, if parallel_max_servers is set to be significantly less than the DOP can the explain plan be sub-optimal?

For tables that have DEGREE DEFAULT, the degree of parallelism (DOP) is calculated by Oracle using number of CPUs and number of threads per CPU amongst other things. As I understand it, when costing ...
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6answers
10k views

CXPACKET Waits performance tune for SQL Server 2008

I have a SQL Server 2008 query that is working on millions of records. The query is w/in a proc that is run nightly by a job. The query can take a full day to run when I first put it on the server, ...
9
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5answers
10k views

Parallelism Best Practices

What are the best practices with setting parallelism in general? I know that SQL Server defaults to 0 to use all available processors, but in what instance would you want to change this default ...
3
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1answer
1k views

Does the pgpool-II extension allow for parallel execution of any query?

I read about pgpool-II here and it states that: Using the parallel query function, data can be divided among the multiple servers, so that a query can be executed on all the servers concurrently to ...
3
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1answer
723 views

Query Parallelism

I have a long running query that behaves differently between two different machines. I have an 8 core machine running Microsoft SQL Server Developer Edition (64-bit) that does not use parallelism and ...
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2answers
1k views

A query submitted from different applications has differing DOP

I have a query which selects from multiple views and is fairly I/O heavy. If I execute this query using Management Studio it uses parallelism across most of the 16 CPUs and completes in under 10 ...
2
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1answer
258 views

Why am I not seeing any benefits of parallel execution when parallel clause is used?

I have these two methods of creating a table and populating with rows. The first one uses a parallel (degree 3) clause, so I expected the inserts to be much faster. But I timed the time taken for a) ...
8
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4answers
6k views

Why are so many MPP solutions based on PostgreSQL instead of MySQL?

Astor Data, Greenplum and GridSQL all allow Massive Parallel Processing of SQL queries. They are also all built around PostgreSQL technology. Is this just because of licensing issues or are there ...
7
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1answer
1k views

How does MS SQL Server decide when it can use “Parallelism” when executing queries?

How does MS SQL Server decide when it can use "Parallelism" when executing queries? I recently posted another question here that, when looking at the actual execution plan used parallelism when I had ...
4
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2answers
635 views

Bizarre crash in T-SQL - what is it?

What would be a typical situation under which the following error would occur, and what does it mean? Also note that I find myself disconnected from the server when the query fails (but I have not ...

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