org.apache.derby.iapi.sql.depend
Interface DependencyManager

All Known Implementing Classes:
BasicDependencyManager

public interface DependencyManager

Dependency Manager Interface

The dependency manager tracks needs that dependents have of providers. This is a general purpose interface interface which is associated with a DataDictinary object; infact the dependencymanager is really the datadictionary keeping track of dependcies between objects that it handles (descriptors) as well as prepared statements.

The primary example of this is a prepared statement's needs of schema objects such as tables.

Dependencies are used so that we can determine when we need to recompile a statement; compiled statements depend on schema objects like tables and constraints, and may no longer be executable when those tables or constraints are altered. For example, consider an insert statement.

An insert statement is likely to have dependencies on the table it inserts into, any tables it selects from (including subqueries), the authorities it uses to do this, and any constraints or triggers it needs to check.

A prepared insert statement has a dependency on the target table of the insert. When it is compiled, that dependency is registered from the prepared statement on the data dictionary entry for the table. This dependency is added to the prepared statement's dependency list, which is also accessible from an overall dependency pool.

A DDL statement will mark invalid any prepared statement that depends on the schema object the DDL statement is altering or dropping. We tend to want to track at the table level rather than the column or constraint level, so that we are not overburdened with dependencies. This does mean that we may invalidate when in fact we do not need to; for example, adding a column to a table may not actually cause an insert statement compiled for that table to stop working; but our level of granularity may force us to invalidate the insert because it has to invalidate all statements that depend on the table due to some of them actually no longer being valid. It is up to the user of the dependency system at what granularity to track dependencies, where to hang them, and how to identify when objects become invalid. The dependency system is basically supplying the ability to find out who is interested in knowing about other, distinct operations. The primary user is the language system, and its primary use is for invalidating prepared statements when DDL occurs.

The insert will recompile itself when its next execution is requested (not when it is invalidated). We don't want it to recompile when the DDL is issued, as that would increase the time of execution of the DDL command unacceptably. Note that the DDL command is also allowed to proceed even if it would make the statement no longer compilable. It can be useful to have a way to recompile invalid statements during idle time in the system, but our first implementation will simply recompile at the next execution.

The start of a recompile will release the connection to all dependencies when it releases the activation class and generates a new one.

The Dependency Manager is capable of storing dependencies to ensure that other D.M.s can see them and invalidate them appropriately. The dependencies in memory only the current D.M. can see; the stored dependencies are visible to other D.M.s once the transaction in which they were stored is committed.

REVISIT: Given that statements are compiled in a separate top-transaction from their execution, we may need/want some intermediate memory storage that makes the dependencies visible to all D.M.s in the system, without requiring that they be stored.

To ensure that dependencies are cleaned up when a statement is undone, the compiler context needs to keep track of what dependent it was creating dependencies for, and if it is informed of a statement exception that causes it to throw out the statement it was compiling, it should also call the dependency manager to have the dependencies removed.

Several expansions of the basic interface may be desirable:

To provide a simple interface that satisfies the basic need, and yet supply more advanced functionality as well, we will present the simple functionality as defaults and provide ways to specify the more advanced functionality.

        interface Dependent {
                boolean isValid();
                InvalidType getInvalidType(); // returns what it sees
                                                // as the "most important"
                                                // of its invalid types.
                void makeInvalid( );
                void makeInvalid( DependencyType dt, InvalidType it );
                void makeValid();
        }

        interface Provider() {
        }

        interface Dependency() {
                Provider getProvider();
                Dependent getDependent();
                DependencyType getDependencyType();
                boolean isValid();
                InvalidType getInvalidType(); // returns what it sees
                                                // as the "most important"
                                                // of its invalid types.
        }

        interface DependencyManager() {
                void addDependency(Dependent d, Provider p, ContextManager cm);
                void invalidateFor(Provider p);
                void invalidateFor(Provider p, DependencyType dt, InvalidType it);
                void clearDependencies(Dependent d);
                void clearDependencies(Dependent d, DependencyType dt);
                Enumeration getProviders (Dependent d);
                Enumeration getProviders (Dependent d, DependencyType dt);
                Enumeration getInvalidDependencies (Dependent d, 
                        DependencyType dt, InvalidType it);
                Enumeration getDependents (Provider p);
                Enumeration getDependents (Provider p, DependencyType dt);
                Enumeration getInvalidDependencies (Provider p, 
                        DependencyType dt, InvalidType it);
        }
        

The simplest things for DependencyType and InvalidType to be are integer id's or strings, rather than complex objects.

In terms of ensuring that no makeInvalid calls are made until we have identified all objects that could be, so that the calls will be made from "leaf" invalid objects (those not in turn relied on by other dependents) to dependent objects upon which others depend, the dependency manager will need to maintain an internal queue of dependencies and make the calls once it has completes its analysis of the dependencies of which it is aware. Since it is much simpler and potentially faster for makeInvalid calls to be made as soon as the dependents are identified, separate implementations may be called for, or separate interfaces to trigger the different styles of invalidation.

In terms of separate interfaces, the DependencyManager might have two methods,

                void makeInvalidImmediate();
                void makeInvalidOrdered();
        
or a flag on the makeInvalid method to choose the style to use.

In terms of separate implementations, the ImmediateInvalidate manager might have simpler internal structures for tracking dependencies than the OrderedInvalidate manager.

The language system doesn't tend to suffer from this ordering problem, as it tends to handle the impact of invalidation by simply deferring recompilation until the next execution. So, a prepared statement might be invalidated several times by a transaction that contains several DDL operations, and only recompiled once, at its next execution. This is sufficient for the common use of a system, where DDL changes tend to be infrequent and clustered.

There could be ways to push this "ordering problem" out of the dependency system, but since it knows when it starts and when it finished finding all of the invalidating actions, it is likely the best home for this.

One other problem that could arise is multiple invalidations occurring one after another. The above design of the dependency system can really only react to each invalidation request as a unit, not to multiple invalidation requests.

Another extension that might be desired is for the dependency manager to provide for cascading invalidations -- that is, if it finds and marks one Dependent object as invalid, if that object can also be a provider, to look for its dependent objects and cascade the dependency on to them. This can be a way to address the multiple-invalidation request need, if it should arise. The simplest way to do this is to always cascade the same invalidation type; otherwise, dependents need to be able to say what a certain type of invalidation type gets changed to when it is handed on.

The basic language system does not need support for cascaded dependencies -- statements do not depend on other statements in a way that involves the dependency system.

I do not know if it would be worthwhile to consider using the dependency manager to aid in the implementation of the SQL DROP statements or not. SQL DROP statements tend to have CASCADE or RESTRICT actions, where they either also DROP all objects that somehow use or depend on the object being dropped, or refuse to drop the object if any such objects exist. Past implementations of database systems have not used the dependency system to implement this functionality, but have instead hard-coded the lookups like so:

                in DropTable:
                        scan the TableAuthority table looking for authorities on
                this table; drop any that are found.
                        scan the ColumnAuthority table looking for authorities on
                this table; drop any that are found.
                        scan the View table looking for views on
                this table; drop any that are found.
                        scan the Column table looking for rows for columns of
                this table; drop any that are found.
                        scan the Constraint table looking for rows for constraints of
                this table; drop any that are found.
                        scan the Index table looking for rows for indexes of
                this table; drop the indexes, and any rows that are found.
                drop the table's conglomerate
                drop the table's row in the Table table.
                

The direct approach such as that outlined in the example will probably be quicker and is definitely "known technology" over the use of a dependency system in this area.


Field Summary
static int ALTER_TABLE
           
static int BULK_INSERT
           
static int CHANGED_CURSOR
           
static int COMPILE_FAILED
           
static int COMPRESS_TABLE
           
static int CREATE_CONSTRAINT
           
static int CREATE_INDEX
           
static int CREATE_TRIGGER
           
static int CREATE_VIEW
           
static int DROP_COLUMN
           
static int DROP_COLUMN_CASCADE
           
static int DROP_CONSTRAINT
           
static int DROP_INDEX
           
static int DROP_JAR
           
static int DROP_METHOD_ALIAS
           
static int DROP_SCHEMA
           
static int DROP_SPS
           
static int DROP_STATISTICS
           
static int DROP_TABLE
           
static int DROP_TABLE_CASCADE
           
static int DROP_TRIGGER
           
static int DROP_VIEW
           
static int DROP_VIEW_CASCADE
           
static int INTERNAL_RECOMPILE_REQUEST
           
static int MAX_ACTION_CODE
          Extensions to this interface may use action codes > MAX_ACTION_CODE without fear of clashing with action codes in this base interface.
static int MODIFY_COLUMN_DEFAULT
           
static int PREPARED_STATEMENT_RELEASE
           
static int RENAME
           
static int RENAME_INDEX
           
static int REPLACE_JAR
           
static int ROLLBACK
           
static int SET_CONSTRAINTS_DISABLE
           
static int SET_CONSTRAINTS_ENABLE
           
static int SET_TRIGGERS_DISABLE
           
static int SET_TRIGGERS_ENABLE
           
static int TRUNCATE_TABLE
           
static int UPDATE_STATISTICS
           
static int USER_RECOMPILE_REQUEST
           
 
Method Summary
 void addDependency(Dependent d, Provider p, ContextManager cm)
          adds a dependency from the dependent on the provider.
 void clearColumnInfoInProviders(ProviderList pl)
          Clear the in memory column bit map information in any table descriptor provider in a provider list.
 void clearDependencies(LanguageConnectionContext lcc, Dependent d)
          Erases all of the dependencies the dependent has, be they valid or invalid, of any dependency type.
 void clearInMemoryDependency(Dependency dy)
          Clear the specified in memory dependency.
 void copyDependencies(Dependent copy_From, Dependent copyTo, boolean persistentOnly, ContextManager cm)
          Copy dependencies from one dependent to another.
 int countDependencies()
          Count the number of active dependencies, both stored and in memory, in the system.
 java.lang.String dumpDependencies()
          Dump out debugging info on all of the dependencies currently within the system.
 java.lang.String getActionString(int action)
          Returns a string representation of the SQL action, hence no need to internationalize, which is causing the invokation of the Dependency Manager.
 ProviderInfo[] getPersistentProviderInfos(Dependent dependent)
          Get a new array of ProviderInfos representing all the persistent providers for the given dependent.
 ProviderInfo[] getPersistentProviderInfos(ProviderList pl)
          Get a new array of ProviderInfos representing all the persistent providers from the given list of providers.
 void invalidateFor(Provider p, int action, LanguageConnectionContext lcc)
          mark all dependencies on the named provider as invalid.
 

Field Detail

COMPILE_FAILED

public static final int COMPILE_FAILED
See Also:
Constant Field Values

DROP_TABLE

public static final int DROP_TABLE
See Also:
Constant Field Values

DROP_INDEX

public static final int DROP_INDEX
See Also:
Constant Field Values

CREATE_INDEX

public static final int CREATE_INDEX
See Also:
Constant Field Values

ROLLBACK

public static final int ROLLBACK
See Also:
Constant Field Values

CHANGED_CURSOR

public static final int CHANGED_CURSOR
See Also:
Constant Field Values

DROP_METHOD_ALIAS

public static final int DROP_METHOD_ALIAS
See Also:
Constant Field Values

DROP_VIEW

public static final int DROP_VIEW
See Also:
Constant Field Values

CREATE_VIEW

public static final int CREATE_VIEW
See Also:
Constant Field Values

PREPARED_STATEMENT_RELEASE

public static final int PREPARED_STATEMENT_RELEASE
See Also:
Constant Field Values

ALTER_TABLE

public static final int ALTER_TABLE
See Also:
Constant Field Values

DROP_SPS

public static final int DROP_SPS
See Also:
Constant Field Values

USER_RECOMPILE_REQUEST

public static final int USER_RECOMPILE_REQUEST
See Also:
Constant Field Values

BULK_INSERT

public static final int BULK_INSERT
See Also:
Constant Field Values

DROP_JAR

public static final int DROP_JAR
See Also:
Constant Field Values

REPLACE_JAR

public static final int REPLACE_JAR
See Also:
Constant Field Values

DROP_CONSTRAINT

public static final int DROP_CONSTRAINT
See Also:
Constant Field Values

SET_CONSTRAINTS_ENABLE

public static final int SET_CONSTRAINTS_ENABLE
See Also:
Constant Field Values

SET_CONSTRAINTS_DISABLE

public static final int SET_CONSTRAINTS_DISABLE
See Also:
Constant Field Values

CREATE_CONSTRAINT

public static final int CREATE_CONSTRAINT
See Also:
Constant Field Values

INTERNAL_RECOMPILE_REQUEST

public static final int INTERNAL_RECOMPILE_REQUEST
See Also:
Constant Field Values

DROP_TRIGGER

public static final int DROP_TRIGGER
See Also:
Constant Field Values

CREATE_TRIGGER

public static final int CREATE_TRIGGER
See Also:
Constant Field Values

SET_TRIGGERS_ENABLE

public static final int SET_TRIGGERS_ENABLE
See Also:
Constant Field Values

SET_TRIGGERS_DISABLE

public static final int SET_TRIGGERS_DISABLE
See Also:
Constant Field Values

MODIFY_COLUMN_DEFAULT

public static final int MODIFY_COLUMN_DEFAULT
See Also:
Constant Field Values

DROP_SCHEMA

public static final int DROP_SCHEMA
See Also:
Constant Field Values

COMPRESS_TABLE

public static final int COMPRESS_TABLE
See Also:
Constant Field Values

RENAME

public static final int RENAME
See Also:
Constant Field Values

DROP_TABLE_CASCADE

public static final int DROP_TABLE_CASCADE
See Also:
Constant Field Values

DROP_VIEW_CASCADE

public static final int DROP_VIEW_CASCADE
See Also:
Constant Field Values

DROP_COLUMN

public static final int DROP_COLUMN
See Also:
Constant Field Values

DROP_COLUMN_CASCADE

public static final int DROP_COLUMN_CASCADE
See Also:
Constant Field Values

DROP_STATISTICS

public static final int DROP_STATISTICS
See Also:
Constant Field Values

UPDATE_STATISTICS

public static final int UPDATE_STATISTICS
See Also:
Constant Field Values

RENAME_INDEX

public static final int RENAME_INDEX
See Also:
Constant Field Values

TRUNCATE_TABLE

public static final int TRUNCATE_TABLE
See Also:
Constant Field Values

MAX_ACTION_CODE

public static final int MAX_ACTION_CODE
Extensions to this interface may use action codes > MAX_ACTION_CODE without fear of clashing with action codes in this base interface.

See Also:
Constant Field Values
Method Detail

addDependency

public void addDependency(Dependent d,
                          Provider p,
                          ContextManager cm)
                   throws StandardException
adds a dependency from the dependent on the provider. This will be considered to be the default type of dependency, when dependency types show up.

Implementations of addDependency should be fast -- performing alot of extra actions to add a dependency would be a detriment.

Parameters:
d - the dependent
p - the provider
cm - Current ContextManager
Throws:
StandardException - thrown if something goes wrong

invalidateFor

public void invalidateFor(Provider p,
                          int action,
                          LanguageConnectionContext lcc)
                   throws StandardException
mark all dependencies on the named provider as invalid. When invalidation types show up, this will use the default invalidation type. The dependencies will still exist once they are marked invalid; clearDependencies should be used to remove dependencies that a dependent has or provider gives.

Implementations of this can take a little time, but are not really expected to recompile things against any changes made to the provider that caused the invalidation. The dependency system makes no guarantees about the state of the provider -- implementations can call this before or after actually changing the provider to its new state.

Implementations should throw DependencyStatementException if the invalidation should be disallowed.

Parameters:
p - the provider
action - The action causing the invalidate
lcc - The LanguageConnectionContext
Throws:
StandardException - thrown if unable to make it invalid

clearDependencies

public void clearDependencies(LanguageConnectionContext lcc,
                              Dependent d)
                       throws StandardException
Erases all of the dependencies the dependent has, be they valid or invalid, of any dependency type. This action is usually performed as the first step in revalidating a dependent; it first erases all the old dependencies, then revalidates itself generating a list of new dependencies, and then marks itself valid if all its new dependencies are valid.

There might be a future want to clear all dependencies for a particular provider, e.g. when destroying the provider. However, at present, they are assumed to stick around and it is the responsibility of the dependent to erase them when revalidating against the new version of the provider.

clearDependencies will delete dependencies if they are stored; the delete is finalized at the next commit.

Parameters:
d - the dependent
Throws:
StandardException - Thrown on failure

clearInMemoryDependency

public void clearInMemoryDependency(Dependency dy)
Clear the specified in memory dependency. This is useful for clean-up when an exception occurs. (We clear all in-memory dependencies added in the current StatementContext.) This method will handle Dependency's that have already been removed from the DependencyManager.


getPersistentProviderInfos

public ProviderInfo[] getPersistentProviderInfos(Dependent dependent)
                                          throws StandardException
Get a new array of ProviderInfos representing all the persistent providers for the given dependent.

Throws:
StandardException - Thrown on error.

getPersistentProviderInfos

public ProviderInfo[] getPersistentProviderInfos(ProviderList pl)
                                          throws StandardException
Get a new array of ProviderInfos representing all the persistent providers from the given list of providers.

Throws:
StandardException - Thrown on error.

clearColumnInfoInProviders

public void clearColumnInfoInProviders(ProviderList pl)
                                throws StandardException
Clear the in memory column bit map information in any table descriptor provider in a provider list. This function needs to be called before the table descriptor is reused as provider in column dependency. For example, this happens in "create publication" statement with target-only DDL where more than one views are defined and they all reference one table.

Throws:
StandardException - Thrown on error.

copyDependencies

public void copyDependencies(Dependent copy_From,
                             Dependent copyTo,
                             boolean persistentOnly,
                             ContextManager cm)
                      throws StandardException
Copy dependencies from one dependent to another.

Parameters:
copy_From - the dependent to copy from
copyTo - the dependent to copy to
persistentOnly - only copy persistent dependencies
cm - Current ContextManager
Throws:
StandardException - Thrown on error.

getActionString

public java.lang.String getActionString(int action)
Returns a string representation of the SQL action, hence no need to internationalize, which is causing the invokation of the Dependency Manager.

Returns:
String The String representation

countDependencies

public int countDependencies()
                      throws StandardException
Count the number of active dependencies, both stored and in memory, in the system.

Returns:
int The number of active dependencies in the system.
Throws:
StandardException - thrown if something goes wrong

dumpDependencies

public java.lang.String dumpDependencies()
                                  throws StandardException,
                                         java.sql.SQLException
Dump out debugging info on all of the dependencies currently within the system.

Returns:
String Debugging info on the dependencies. (null if SanityManger.DEBUG is false)
Throws:
StandardException - thrown if something goes wrong
java.sql.SQLException - thrown if something goes wrong


Apache Derby V10.0 Engine Documentation - Copyright © 1997,2004 The Apache Software Foundation or its licensors, as applicable.