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Support value distribution histograms [CORE1686] #2111
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Modified by: @dyemanovassignee: Dmitry Yemanov [ dimitr ] |
Modified by: @pcisarWorkflow: jira [ 13813 ] => Firebird [ 14121 ] |
Commented by: @dyemanov Suggested by Bill Oliver: When this is added I would like to see the histogram information available through the monitoring tables, too. Information that might be surfaced might include: - Column's Most Common Value (MCV) |
Modified by: @dyemanovFix Version: 3.0 Alpha 1 [ 10331 ] |
Commented by: Philip Williams (unordained) Is NULL handled as a special case in the histogram? Can other values be requested to be treated as special, for situations where you know a field is being abused with special values (e.g. the field has a very regular distribution, except for the values -1, 0, and 1, which are each individually special and very different from > 1.) |
Commented by: @krilbe In ref to Philip Williams' comment: I vote strongly for treating null as a special case in the histogram, i.e. always keep a specific frequency/selectivity figure for null, if the indexed column allows null. For a compound index, I'm not quite sure how to handle cases where some columns are null and some are not, but i assume that the all-null case should be treated separately, i.e. like null for a single-column index. |
Commented by: @dyemanov Yes, nulls are to be treated separately. |
Modified by: @dyemanovFix Version: 3.0 Beta 2 [ 10586 ] => |
Commented by: Atri Sharma (atris) Hi, I am a relational database developer, focused on many areas. I would like to start hacking Firebird,with this issue, if possible. Please advice. |
Commented by: Ann Harrison (awharrison) Histograms are less useful in database like Firebird that optimize queries Select c.zipcode |
Modified by: @dyemanovFix Version: 4.0 Alpha 1 [ 10731 ] |
Modified by: @dyemanovFix Version: 4.0 Beta 1 [ 10750 ] => |
Databases I deal with includes both NULLs and EMPTY strings. It is not feasible to convert EMTPY strings to NULLs because the risk that applications start giving errors. I'm read in a recent discussion that histograms might be of help for EMPTY string values. |
Submitted by: Timo Partanen (partim)
Is duplicated by CORE2381
Relate to CORE4666
Votes: 12
To provide better performance for queries, Firebird should support value distribution histograms. A histogram is a statistical report that shows the frequency of values within steps or ranges of values that fall between a certain minimum and maximum. Generally, histograms improve the performance of queries because the optimizer can use them to estimate the selectivity of conditions better than from the selectivity of indexes.
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