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https://issues.apache.org/jira/browse/DERBY-5799?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kim Haase updated DERBY-5799:
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Issue & fix info: Patch Available
Affects Version/s: 10.9.1.0
> add more info on when Derby chooses 32k page size for tables.
> -------------------------------------------------------------
>
> Key: DERBY-5799
> URL: https://issues.apache.org/jira/browse/DERBY-5799
> Project: Derby
> Issue Type: Improvement
> Components: Documentation
> Affects Versions: 10.8.2.2, 10.9.1.0
> Reporter: Mike Matrigali
> Assignee: Kim Haase
> Priority: Minor
> Attachments: DERBY-5799.diff, rrefproper40688.html
>
>
> Enhance the following documentation to explain all cases when Derby will
> default a table to 32k.
> current doc:
> http://db.apache.org/derby/docs/10.8/ref/rrefproper40688.html
> 1) better describe what "long" means. Originally this was clear as it meant
> just datatypes with
> the "long" qualifier. Now it also includes Blob and Clob columns. Not sure
> if we should list
> all the types, or just something like long, Blob and/or Clob.
> 2) Derby will also choose 32k if the approximate length of the columns
> declared at create time is greater than 4k. Approximate is used as each
> different datatype may or may not be fixed length
> when stored on the page. Character data may take 1, 2, or 3 bytes per
> character, obviously
> variable length data like varchar can't be known at create time, ...
> I don't think we should try to document exact derby algorithm, rather doc
> that Derby will default
> to what it thinks should be the best size of either 4k or 32k unless user
> chooses to override. I
> do think it is useful to doc that Derby will include both existence of long
> columns and the estimate
> length of the row.
> Here some comments from Property.java that describes constants used, if these
> constants every change then documentation would change also:
> /**
> * The default page size to use for tables that contain a long column.
> **/
> public static final String PAGE_SIZE_DEFAULT_LONG = "32768";
> /**
> * The bump threshold for pages sizes for create tables
> * If the approximate column sizes of a table is greater than this
> * threshold, the page size for the tbl is bumped to
> PAGE_SIZE_DEFAULT_LONG
> * provided the page size is not already specified as a property
> **/
> public static final int TBL_PAGE_SIZE_BUMP_THRESHOLD = 4096;
> /**
> * The bump threshold for pages size for index.
> * If the approximate key columns of an index is greater than this
> * threshold, the page size for the index is bumped to
> PAGE_SIZE_DEFAULT_LON
> G
> * provided the page size is not already specified as a property
> **/
> public static final int IDX_PAGE_SIZE_BUMP_THRESHOLD = 1024;
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