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What is the significance of the columnstore_segment_rows variable? What is the effect of maintaining it at a high or low level?
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The columnstore_segment_rows variable controls the number of rows in each segment of a Columnstore table. The default value is 1,024,000, and the maximum allowed is 10,000,000. This setting can be configured at the cluster level or overridden per table.
Impact of Different Values from the Default:
Higher columnstore_segment_rows (Larger segments):
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Pros:
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Better compression due to larger data chunks.
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Faster table scans, especially for non-selective queries.
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Reduced disk usage overall.
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Cons:
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May reduce the effectiveness of segment elimination for selective queries.
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Lower columnstore_segment_rows (Smaller segments):
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Pros:
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Improved segment elimination enhances performance in selective queries.
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Cons:
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Lower compression efficiency.
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More metadata overhead and higher memory usage.
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Increased random I/O during non-selective scans, due to many smaller blobs.
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Choosing the right value depends on your workload. Analytical workloads with large scans may benefit from higher values, while workloads with frequent selective filters might perform better with lower values.
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