Class SequenceUpdater
- java.lang.Object
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- org.apache.derby.impl.sql.catalog.SequenceUpdater
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- All Implemented Interfaces:
Cacheable
- Direct Known Subclasses:
SequenceUpdater.BulkInsertUpdater
,SequenceUpdater.SyssequenceUpdater
public abstract class SequenceUpdater extends java.lang.Object implements Cacheable
An object cached in the data dictionary which manages new values for sequences. Note that this class must be public and have a 0-arg constructor in order to satisfy the Cacheable contract.
This is the abstract superclass of specific implementations for specific sequences. For instance, one subclass handles the ANSI/ISO sequences stored in SYSSEQUENCES. Another subclass could handle the sequences stored in Derby's identity columns.
This class does a couple tricky things:
- It pre-allocates a range of values from a sequence so that we don't have to change the on-disk value every time we get the next value for a sequence.
- When updating the on-disk value, we use a subtransaction of the user's execution transaction. If the special transaction cannot do its work immediately, without waiting for a lock, then a TOO MUCH CONTENTION error is raised. It is believed that this can only happen if someone holds locks on SYSSEQUENCES, either via sequence DDL or a scan of the catalog. The TOO MUCH CONTENTION error tells the user to not scan SYSSEQUENCES directly, but to instead use the SYSCS_UTIL.SYSCS_PEEK_AT_SEQUENCE() if the user needs the current value of the sequence generator.
Here is the algorithm pursued when the caller asks for the next number in a sequence:
- We try to get the next number from a cache of pre-allocated numbers. The endpoint (last number in the pre-allocated range) was previously recorded in the catalog row which describes this sequence. If we are successful in getting the next number, we return it and all is well.
- Otherwise, we must allocate a new range by updating the catalog row. We should not be in contention with another connection because the update method is synchronized.
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
SequenceUpdater.BulkInsertUpdater
Implementation of SequenceUpdater for use with the bulk-insert optimization used by InsertResultSet.static class
SequenceUpdater.SyssequenceUpdater
Specific implementation of SequenceUpdater for the sequences managed by SYSSEQUENCES.
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Field Summary
Fields Modifier and Type Field Description protected DataDictionaryImpl
_dd
protected SequenceGenerator
_sequenceGenerator
This is the object which allocates ranges of sequence valuesprotected java.lang.String
_uuidString
This is the key used to lookup this generator in the cache.
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Constructor Summary
Constructors Constructor Description SequenceUpdater()
No-arg constructor to satisfy the Cacheable contractSequenceUpdater(DataDictionaryImpl dd)
Normal constructor
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Method Summary
All Methods Static Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description void
clean(boolean forRemove)
Clean the object.void
clearIdentity()
Put the object into the No Identity state.Cacheable
createIdentity(java.lang.Object key, java.lang.Object createParameter)
Create a new item.protected abstract SequenceGenerator
createSequenceGenerator(TransactionController readOnlyTC)
Initialize the sequence generator.SequenceUpdater.BulkInsertUpdater
getBulkInsertUpdater(boolean restart)
Get the SequenceUpdater used for the bulk-insert optimization in InsertResultSet.private static Context
getContextOrNull(java.lang.String contextID)
Privileged lookup of a Context.private static ContextService
getContextService()
Privileged lookup of the ContextService.void
getCurrentValueAndAdvance(NumberDataValue returnValue)
Get the next sequence number managed by this generator and advance the number.java.lang.Object
getIdentity()
Get the identity of this object.private static LanguageConnectionContext
getLCC()
boolean
isDirty()
Returns true of the object is dirty.private boolean
isNumber(java.lang.String text)
protected SequencePreallocator
makePreallocator(TransactionController tc)
Make a new range allocator (called when the generator is instantiated)private StandardException
missingAllocator(java.lang.String propertyName, java.lang.String className, java.lang.Exception e)
java.lang.Long
peekAtCurrentValue()
Get the current value of the sequence generator without advancing it.void
reset(java.lang.Long newValue)
Reset the sequence generator to a new start value.Cacheable
setIdentity(java.lang.Object key)
Set the identity of the object.private StandardException
tooMuchContentionException()
Create an exception to state that there is too much contention on the generator.private StandardException
unimplementedFeature()
Report an unimplemented featureboolean
updateCurrentValueOnDisk(java.lang.Long oldValue, java.lang.Long newValue)
Update the value on disk.protected abstract boolean
updateCurrentValueOnDisk(TransactionController tc, java.lang.Long oldValue, java.lang.Long newValue, boolean wait)
Update the sequence value on disk.
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Field Detail
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_dd
protected DataDictionaryImpl _dd
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_uuidString
protected java.lang.String _uuidString
This is the key used to lookup this generator in the cache.
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_sequenceGenerator
protected SequenceGenerator _sequenceGenerator
This is the object which allocates ranges of sequence values
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Constructor Detail
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SequenceUpdater
public SequenceUpdater()
No-arg constructor to satisfy the Cacheable contract
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SequenceUpdater
public SequenceUpdater(DataDictionaryImpl dd)
Normal constructor
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Method Detail
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createSequenceGenerator
protected abstract SequenceGenerator createSequenceGenerator(TransactionController readOnlyTC) throws StandardException
Initialize the sequence generator. Work is done inside a read-only subtransaction of the session's execution transaction.
- Throws:
StandardException
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updateCurrentValueOnDisk
protected abstract boolean updateCurrentValueOnDisk(TransactionController tc, java.lang.Long oldValue, java.lang.Long newValue, boolean wait) throws StandardException
Update the sequence value on disk. This method does its work in a subtransaction of the user's execution transaction.
- Parameters:
tc
- The transaction to useoldValue
- Expected value on disk for this sequencenewValue
- The value to poke into the system table backing this sequencewait
- Whether to wait for a lock- Returns:
- Returns true if the value was successfully updated, false if we lost a race with another session.
- Throws:
StandardException
- May throw an exception if a lock can't be obtained.
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tooMuchContentionException
private StandardException tooMuchContentionException()
Create an exception to state that there is too much contention on the generator. For backward compatibility reasons, different messages are needed by sequences and identities. See DERBY-5426.
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clean
public void clean(boolean forRemove) throws StandardException
Description copied from interface:Cacheable
Clean the object. It is up to the object to ensure synchronization of the isDirty() and clean() method calls.
If forRemove is true then the object is being removed due to an explict remove request, in this case the cache manager will have called this method regardless of the state of the isDirty()
If an exception is thrown the object must be left in the clean state.
MT - thread safe - Can be called at any time by the cache manager, it is the responsibility of the object implementing Cacheable to ensure any users of the object do not conflict with the clean call.- Specified by:
clean
in interfaceCacheable
- Throws:
StandardException
- Standard Derby error policy.
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isDirty
public boolean isDirty()
Description copied from interface:Cacheable
Returns true of the object is dirty. May be called when the object is kept or unkept.
MT - thread safe
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getIdentity
public java.lang.Object getIdentity()
Description copied from interface:Cacheable
Get the identity of this object.
MT - thread safe.- Specified by:
getIdentity
in interfaceCacheable
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clearIdentity
public void clearIdentity()
Description copied from interface:Cacheable
Put the object into the No Identity state.
MT - single thread required - Method must only be called be cache manager and the cache manager will guarantee only one thread can be calling it.- Specified by:
clearIdentity
in interfaceCacheable
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createIdentity
public Cacheable createIdentity(java.lang.Object key, java.lang.Object createParameter) throws StandardException
Description copied from interface:Cacheable
Create a new item.Create a new item and set the identity of the object to represent it. The object will be in the No Identity state, ie. it will have just been created or clearIdentity() was just called.
The object must copy the information out of key, not just store a reference to key if the key is not immutable. After this call the expression getIdentity().equals(key) must return true.
If the class of the object needs to change (e.g. to support a different format) then the object should create a new object, call its initParameter() with the parameters the original object was called with, set its identity and return a reference to it. The cache manager will discard the reference to the old object.
If an exception is thrown the object must be left in the no-identity state.
MT - single thread required - Method must only be called be cache manager and the cache manager will guarantee only one thread can be calling it.- Specified by:
createIdentity
in interfaceCacheable
- Returns:
- an object reference if the object can take on the identity, null otherwise.
- Throws:
StandardException
- If forCreate is true and the object cannot be created.- See Also:
CacheManager.create(java.lang.Object, java.lang.Object)
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setIdentity
public Cacheable setIdentity(java.lang.Object key) throws StandardException
Description copied from interface:Cacheable
Set the identity of the object.Set the identity of the object to represent an item that already exists, e.g. an existing container. The object will be in the No Identity state, ie. it will have just been created or clearIdentity() was just called.
The object must copy the information out of key, not just store a reference to key. After this call the expression getIdentity().equals(key) must return true.
If the class of the object needs to change (e.g. to support a different format) then the object should create a new object, call its initParameter() with the parameters the original object was called with, set its identity and return a reference to it. The cache manager will discard the reference to the old object.
If an exception is thrown the object must be left in the no-identity state.
MT - single thread required - Method must only be called be cache manager and the cache manager will guarantee only one thread can be calling it.- Specified by:
setIdentity
in interfaceCacheable
- Returns:
- an object reference if the object can take on the identity, null otherwise.
- Throws:
StandardException
- Thrown on error- See Also:
Cacheable.setIdentity(java.lang.Object)
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reset
public void reset(java.lang.Long newValue) throws StandardException
Reset the sequence generator to a new start value. This is used by the special bulk-insert optimization in InsertResultSet.
- Throws:
StandardException
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getBulkInsertUpdater
public SequenceUpdater.BulkInsertUpdater getBulkInsertUpdater(boolean restart) throws StandardException
Get the SequenceUpdater used for the bulk-insert optimization in InsertResultSet.
- Parameters:
restart
- True if the counter should be re-initialized to its start position.- Throws:
StandardException
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getCurrentValueAndAdvance
public void getCurrentValueAndAdvance(NumberDataValue returnValue) throws StandardException
Get the next sequence number managed by this generator and advance the number. Could raise an exception if the legal range is exhausted and wrap-around is not allowed. Only one thread at a time is allowed through here. We do not want a race between the two calls to the sequence generator: getCurrentValueAndAdvance() and allocateNewRange().
- Parameters:
returnValue
- This value is stuffed with the new sequence number.- Throws:
StandardException
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peekAtCurrentValue
public java.lang.Long peekAtCurrentValue() throws StandardException
Get the current value of the sequence generator without advancing it. May return null if the generator is exhausted.
- Throws:
StandardException
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updateCurrentValueOnDisk
public boolean updateCurrentValueOnDisk(java.lang.Long oldValue, java.lang.Long newValue) throws StandardException
Update the value on disk. Does its work in a subtransaction of the user's execution transaction. If that fails, raises a TOO MUCH CONTENTION exception.
- Returns:
- Returns true if the value was successfully updated, false if we lost a race with another session.
- Throws:
StandardException
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makePreallocator
protected SequencePreallocator makePreallocator(TransactionController tc) throws StandardException
Make a new range allocator (called when the generator is instantiated)- Throws:
StandardException
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missingAllocator
private StandardException missingAllocator(java.lang.String propertyName, java.lang.String className, java.lang.Exception e)
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isNumber
private boolean isNumber(java.lang.String text)
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getLCC
private static LanguageConnectionContext getLCC()
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unimplementedFeature
private StandardException unimplementedFeature()
Report an unimplemented feature
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getContextService
private static ContextService getContextService()
Privileged lookup of the ContextService. Must be private so that user code can't call this entry point.
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getContextOrNull
private static Context getContextOrNull(java.lang.String contextID)
Privileged lookup of a Context. Must be private so that user code can't call this entry point.
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