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

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Mathematical or Computing Alternatives for MySQL Combination Queries operating toward their Performance Limit

We regularly run a contest that is becoming quite popular. In the contest, we need to select the combinations of contestants from 8 groups whose cost is under a threshold, and who combined have the ...
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42 views

Two servers, different execution plans. Several orders of magnitude difference in run time

Two servers, Development and Live. Live server is an Amazon RDS SQL Server Web instance. Both servers have identical schema and data. There is a good spatial index on the geometry column. On my ...
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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. ...
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Performance differs on same query against two (almost) identical tables?

I'm running these two queries in SQL Server 2012: SELECT tpua.Field1, CAST(round(twg.Field2 * 2, 0) / 2 As Decimal(8,1)) As Field2, CAST((round((twg.Field3/10.0) * 2, 0) / 2) * 10 As int) As ...
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695 views

Oracle parallel query: finding out which Producer a Consumer is waiting for

One of our materialized view refresh's (part of a daily ETL routine) was hanging today; it usually completes within 5 minutes, but this time, I had to kill it after 23 hours. V$SESSION contained this ...
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Parallel insert in db2

I am trying to import from 8 files and insert into a single table in db2. I am running 8 .sql files that will do the task, but only one of them actually seem to be running and inserting into table. ...
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152 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 ...
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MySQL - Update vs. Replace Into — why is Update non-parallel, and Replace Into allows multi-threads?

In trying to optimize a query that does (Insert ... on duplicate key update) .... someone suggested I do "Replace Into" to optimize performance. I'm not 100% certain the difference other than ... ...
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Sql Server, a single threaded query spawns multiple threads (or internal parellelizaion during execution)

In Sql Server, when I run a procedure or a query that takes multiple minutes, sometimes spawns multiple threads. Even though there is no MAXDOP hint or necessity in the query, I see multiple instances ...
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280 views

MySQL Cluster lock wait timeout exceeded when trying to deal with huge amount of queries

I'm trying to deal with many connections and sometime I get following error: ERROR : Lock wait timeout exceeded; try restarting transaction The bigger number of queries the least number of ...