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

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3
votes
2answers
173 views

High CXPACKET and LATCH_EX waits

I am having some performance issues with a data processing system which I am working on. I have gathered wait stats from a one hour peroid which show a large amount of CXPACKET and LATCH_EX wait ...
0
votes
0answers
21 views

Why are there more MySQL deadlocks on my 8-core machine than 16-core?

I'm running a bunch of scripts in parallel that do: START TRANSACTION REPLACE INTO... REPLACE INTO... REPLACE INTO... ... COMMIT On my 8-core machine, where 8 of these processes are running in ...
0
votes
1answer
13 views

Oracle Autodop disabled at the table level

I have a question related to Oracle auto DOP and parallel DML concepts. I have a scenario, if I set the Auto DOP set to 1 on the table and if I run parallel DML statements on that table through ...
5
votes
1answer
306 views

Can a single PostgreSQL query use multiple cores?

In recent versions of PostgreSQL, can we share a query between two or more cores to get a performance boost? Or should we get faster cores?
0
votes
1answer
73 views

How is parallelism threshold (seconds) used if query CPU cost is actually unitless

How does the optimizer decide whether or not to use parallelism when the parallelism threshold is specified in seconds (on specific hardware, see below) but the estimated CPU costs are supposedly ...
1
vote
0answers
115 views

Why does removing a RID by creating a clustered index lose parallelism and slow down execution by 2X

If I remove a RID lookup by replacing 2 non-clustered indices (non unique) with 2 identical clustered indicies (non-unique) where there weren't any before, why does this query slow down by a factor ...
1
vote
1answer
267 views

SSIS 2012 Ftp parallel/asynchronous multiple file download

Any help would be appreciated with either scenario. if Are there any settings available to download multiple files in parallel from an FTP server? else If not, I guess I'll just roll my own via ...
7
votes
2answers
2k views

Need to understand parallel query execution error

Today we experienced a degradation in performance on our production sql server. Durring the time this occurred we logged several "The query processor could not start the necessary thread resources ...
3
votes
1answer
146 views

PLSQL : DBMS Jobs - parallelization?

I am looping over a cursor and executing a stored procedure; how do I parallelize this process through dbms.jobs? for rec in select column from table1 loop execute stored_procedure( rec.column ); end ...
1
vote
1answer
62 views

MySQL: parallel restores at same time from backup files?

Slightly related to this question, but for MySQL: Would it be possible/wise to execute 2 parallel restores from a single backup? Is it possible/wise to do a parallel restore of two independent ...
3
votes
0answers
174 views

Are the following statements concerning sys.dm_exec_requests true?

Parallel plans mean that cpu_time can be greater than total_elapsed time. Therefore, per-query wait time is not possible to determine accurately from DMVs on servers with more than one CPU thread. ...
5
votes
1answer
737 views

Executing SPs in parallel (maybe with a cursor) [closed]

We have an 3rd party accounting system that runs on SQL Server 2008 R2. To insert invoices into this accounting system, we have to use the API that comes with it (which is just a set of encrypted ...
0
votes
1answer
53 views

Oracle scheduler max_jobs_Slave_processes is set to null, how many will be allocated?

Executing the following query against my database: select value from dba_scheduler_global_attribute where attribute_name='MAX_JOB_SLAVE_PROCESSES'; yields a value of NULL. My question is what ...
3
votes
1answer
175 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 ...
6
votes
3answers
913 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 ...
3
votes
2answers
566 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 ...
1
vote
1answer
285 views

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

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 ...
1
vote
2answers
826 views

Is problem with parallelism more common today than before? And what issues can arise from paralellism?

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 ...
9
votes
3answers
3k 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 ...
4
votes
2answers
6k 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
votes
1answer
3k 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 ...
6
votes
6answers
4k 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, ...
5
votes
4answers
3k 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 ...
2
votes
1answer
630 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 ...
3
votes
1answer
592 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 ...
3
votes
2answers
589 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 ...
1
vote
1answer
175 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) ...
5
votes
4answers
2k 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 ...
6
votes
1answer
494 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 ...
3
votes
2answers
181 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 ...