Minor Description
Currently four no-argument diagnostic tables exist that provide information about the running state of Derby, or its error messages.
These tables are invoked using an awkward, non-standard syntax. As an example:
SELECT * FROM NEW org.apache.derby.diag.LockTable() as LOCK_TABLE
The improvement will provide an internal mapping from a regular table name in the SYSCS_DIAG schema
to the runtime virtual table code. Thus the above example would be replaced by:
SELECT * FROM SYSCS_DIAG.LOCK_TABLE
These diagnostic table expressions are regular table expressions (as is the NEW VTI construct) and
can be used wherever a normal table can.
Any DDL, INSERT/UPDATE/DELETE, compression procedure etc. that references a diagnostic table
will result in an exception.
The old style syntax will remain in place for 10.2, but become deprecated.
The tables to be implemented in this change are:
SYSCS_DIAG.LOCK_TABLE replaces org.apache.derby.diag.LockTable
SYSCS_DIAG.STATEMENT_CACHE replaces org.apache.derby.diag.StatementCache
SYSCS_DIAG.TRANSACTION_TABLE replaces org.apache.derby.diag.TransactionTable
SYSCS_DIAG.ERROR_MESSAGES replaces org.apache.derby.diag.ErrorMessages
Adding such a table will be table driven, thus easy for others to provide additional diagnostics.
Information about these diagnostic tables will not appear in the system catalogs or JDBC DatabaseMetaData.
The ResultSetMetaData for the any query involving a diagnostic table will be valid.
This is a first step in a progression towards supporing a fully application/user defined virtual table.
These steps are not part of this jira issue, but added for information purposes.
- second step - supporting diagnostic tables with parameters, e.g.
SELECT * FROM SYSCS_DIAG.SPACE_TABLE('sales', 'orders');
- third step - providing a create virtual table statement (most databases support
some form of virtual table, or wrappers). The DDL would be non-standard but the
data access would be standard. [need to check table functions in part 13 of SQL standard]
E.g. syntax yet to be defined, but to give the general idea
CREATE VIRTUAL TABLE (TICKER VARCHAR(10), START TIMESTAMP, END TIMESTAMP)
LANGUAGE JAVA
PARAMETER STYLE JAVA
EXTERNAL NAME 'com.acme.stocks.historyFromYahooFinance';
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Issue Links
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Document new SYSCS_DIAG tables |
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Closed | Laura Stewart |