- All Known Implementing Classes:
DefaultDiagnosticsListener
- Author:
- Lukas Eder
-
Method Summary
Modifier and TypeMethodDescriptiondefault void
The executed JDBC statement has duplicates.default void
Something went wrong while diagnosing a SQL query.default void
The fetched JDBCResultSet
returned a primitive type value for a column, which could have been null, butResultSet.wasNull()
was not called.default void
The executed JDBC statement is repeated consecutively on the same JDBCConnection
.default void
The fetched JDBCResultSet
returned more columns than necessary.default void
The fetched JDBCResultSet
returned more rows than necessary.default void
A trivial condition was encountered, which can be replaced by aNULL
predicate, or even byDSL.trueCondition()
orDSL.falseCondition()
, but it is more likely just a typo.default void
The fetched JDBCResultSet
returned a value for a column, on whichResultSet.wasNull()
was called unnecessarily (more than once, or for a non-primitive type).
-
Method Details
-
tooManyRowsFetched
The fetched JDBCResultSet
returned more rows than necessary.An event indicating that a JDBC
ResultSet
was fetched withA
rows, but onlyB
rows (B < A
) were consumed.Typically, this problem can be remedied by applying the appropriate
LIMIT
clause in SQL, orSelectLimitStep.limit(Number)
clause in jOOQ.- Parameters:
ctx
- The context containing information about the diagnostic.
-
tooManyColumnsFetched
The fetched JDBCResultSet
returned more columns than necessary.An event indicating that a JDBC
ResultSet
was fetched withA
columns, but onlyB
(B < A
) were consumed.Typically, this problem can be remedied by not running a
SELECT *
query when this isn't strictly required.- Parameters:
ctx
- The context containing information about the diagnostic.
-
unnecessaryWasNullCall
The fetched JDBCResultSet
returned a value for a column, on whichResultSet.wasNull()
was called unnecessarily (more than once, or for a non-primitive type).- Parameters:
ctx
- The context containing information about the diagnostic.
-
missingWasNullCall
The fetched JDBCResultSet
returned a primitive type value for a column, which could have been null, butResultSet.wasNull()
was not called.- Parameters:
ctx
- The context containing information about the diagnostic.
-
duplicateStatements
The executed JDBC statement has duplicates.Many databases maintain an execution plan cache, which remembers execution plans for a given SQL string. These caches often use the verbatim SQL string (or a hash thereof) as a key, meaning that "similar" but not identical statements will produce different keys. This may be desired in rare cases when querying skewed data, as a hack to force the optimiser to calculate a new plan for a given "similar" but not identical query, but mostly, this is not desirable as calculating execution plans can turn out to be expensive.
Examples of such duplicate statements include:
Whitespace differences
SELECT * FROM actor; SELECT * FROM actor;
Inline bind values
SELECT * FROM actor WHERE id = 1; SELECT * FROM actor WHERE id = 2;
Aliasing and qualification
SELECT a1.* FROM actor a1 WHERE id = ?; SELECT * FROM actor a2 WHERE a2.id = ?;
Examples of identical statements (which are not considered duplicate, but
repeatedStatements(DiagnosticsContext)
, if on the sameConnection
) are:SELECT * FROM actor WHERE id = ?; SELECT * FROM actor WHERE id = ?;
This is a system-wide diagnostic that is not specific to individual
Connection
instances.- Parameters:
ctx
- The context containing information about the diagnostic.
-
repeatedStatements
The executed JDBC statement is repeated consecutively on the same JDBCConnection
.This problem goes by many names, the most famous one being the N + 1 problem, when a single (1) query for a parent entity requires many (N) subsequent queries for child entities. This could have been prevented by rewriting the parent query to use a JOIN. If such a rewrite is not possible (or not easy), the subsequent N queries could at least profit (depending on the exact query):
- From reusing the
PreparedStatement
- From being batched
- From being re-written as a bulk fetch or write query
This problem can be aggravated if combined with the
duplicateStatements(DiagnosticsContext)
problem, in case of which the repeated statements might not be diagnosed as easily.Repeated statements may or may not be "identical". In the following example, there are two repeated and identical statements:
SELECT * FROM actor WHERE id = ?; SELECT * FROM actor WHERE id = ?;
In this example, we have three repeated statements, only some of which are also identical:
SELECT * FROM actor WHERE id = ?; SELECT * FROM actor WHERE id = ?; SELECT * FROM actor WHERE id = ?;
This is a
Connection
-specific diagnostic that is reset every timeConnection.close()
is called.- Parameters:
ctx
- The context containing information about the diagnostic.
- From reusing the
-
trivialCondition
A trivial condition was encountered, which can be replaced by aNULL
predicate, or even byDSL.trueCondition()
orDSL.falseCondition()
, but it is more likely just a typo.A trivial condition might compare a column to itself, e.g.
SELECT * FROM actor a JOIN film_actor fa ON a.actor_id = a.actor_id
The above
JOIN
predicate is effectivelya.actor_id IS NOT NULL
, but what the author probably meant was to writea.actor_id = fa.actor_id
instead.This mistake can often be very subtle, especially when comparing columns of composite constraints. In many cases, it's a bug, and if it isn't there's probably a more straightforward way to declare the condition.
- Parameters:
ctx
- The context containing information about the diagnostic.
-
exception
Something went wrong while diagnosing a SQL query.The actual exception will be provided by
DiagnosticsContext.exception()
. Likely exceptions include:- A
ParserException
because jOOQ couldn't parse user defined SQL. - A user exception from a custom
DiagnosticsListener
implementation.
- Parameters:
ctx
- The context containing information about the diagnostic.
- A
-