Memory Grants Affecting Columnstore Load

Denzil Ribeiro explains how memory grant pressure can determine whether a columnstore bulk insert skips the deltastore or not:

We found that only at the beginning of the run, there was contention on memory grants (RESOURCE_SEMAPHORE waits), for a short period of time. After that and later into the process, we could see some latch contention on regular data pages, which we didn’t expect as each thread was supposed to insert into its own row group. You would also see this same data by querying sys.dm_exec_requests live, if you caught it within the first minute of execution, as displayed below.

This is useful in case you run into the issue, but also useful as a case study on effective troubleshooting.

Related Posts

The Transaction Log in Delta Tables

Burak Yavuz, et al, explain how the transaction log works with Delta Tables in Apache Spark: When a user creates a Delta Lake table, that table’s transaction log is automatically created in the _delta_log subdirectory. As he or she makes changes to that table, those changes are recorded as ordered, atomic commits in the transaction log. Each commit […]

Read More

Calculated Columns and Memory Usage in Analysis Services

Teo Lachev troubleshoots a customer issue: Scenario: A client reports a memory spike during processing. They have a Tabular semantic model deployed to Azure Analysis Services. They fully process the model daily. The model normally takes less than 50 GB RAM but during processing, it spikes five times and Azure Analysis Services terminates the processing task […]

Read More

Categories

June 2017
MTWTFSS
« May Jul »
 1234
567891011
12131415161718
19202122232425
2627282930