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Key: CORE-3295
Type: Improvement Improvement
Status: Closed Closed
Resolution: Fixed
Priority: Major Major
Assignee: Dmitry Yemanov
Reporter: Dmitry Yemanov
Votes: 0
Watchers: 0
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Firebird Core

Estimate the actual record compression ratio in the optimizer

Created: 28/Dec/10 11:53 AM   Updated: 04/Feb/11 12:58 PM
Component/s: Engine
Affects Version/s: None
Fix Version/s: 2.1.4, 2.5.1

Time Tracking:
Not Specified

Planning Status: Unspecified


 Description  « Hide
Currently, when the table cardinality (number of records) gets estimated, all records are considered to be compressed twice in size (hardcoded compression ratio of 0.5). It would be better to have some estimation (even rough) of the actual compression ratio, because in practice it can differ much from the expected value. This becomes more important starting with versions 2.1.4 and 2.5.0 that have the join cost more depending on the proper cardinality estimations than in prior versions.

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