Package io.permazen.kv

Interface KVStore

All Known Subinterfaces:

AtomicKVStore, CloseableKVStore, KVTransaction, ReadTracking

All Known Implementing Classes:

AbstractKVStore, ArrayKVStore, ArrayKVTransaction, AtomicArrayKVStore, AtomicKVDatabase, BerkeleyKVTransaction, ByteArrayLMDBKVStore, ByteArrayLMDBKVTransaction, CachingKVStore, CachingKVTransaction, CloseableForwardingKVStore, FallbackKVTransaction, ForwardingKVStore, FoundationKVStore, FoundationKVTransaction, LevelDBAtomicKVStore, LevelDBKVStore, LevelDBKVTransaction, LMDBKVStore, LMDBKVTransaction, MutableView, MVMapKVStore, MVMapSnapshot, MVStoreAtomicKVStore, MVStoreKVTransaction, NavigableMapKVStore, PrefixKVStore, PrefixKVTransaction, RaftKVTransaction, ReadOnlySpannerView, ReadWriteSpannerView, RocksDBAtomicKVStore, RocksDBKVStore, RocksDBKVTransaction, SimpleKVTransaction, SnapshotKVTransaction, SnapshotLevelDBKVStore, SnapshotRocksDBKVStore, SpannerKVTransaction, SQLKVTransaction, UnmodifiableKVStore, XMLKVTransaction, XodusKVStore, XodusKVTransaction

public interface KVStore

General API into a key/value store where the keys are sorted lexicographically as unsigned bytes.

Implementations are not required to support accessing keys that start with 0xff, and if not may throw IllegalArgumentException if such keys are accessed.

Thread Safety

Instances must be thread safe, with the exception of the Iterator returned by getRange().

Lock-free Counters

Implementations are encouraged to include support for encoding a 64 bit counter in a key/value pair such that the counter can be efficiently adjusted by concurrent transactions without conflict. In practice this means no locking is required to increment or decrement the counter by some amount, as long as it's not necessary to actually directly read or write the counter value in the same transaction. Whether counter adjustments are actually lock-free is implementation dependent, however, the counter methods encodeCounter(), decodeCounter(), and adjustCounter() must function correctly as specified in all cases.

How counters are encoded is specific to the implementation. Clients needing to read or write counter values directly should use decodeCounter() and encodeCounter(), respectively. Counters are removed using the normal methods (i.e., remove() and removeRange()).

Method Summary

Modifier and Type	Method	Description
void	adjustCounter(byte[] key, long amount)	Adjust the counter at the given key by the given amount.
default void	apply(Mutations mutations)	Apply all the given Mutations to this instance.
long	decodeCounter(byte[] value)	Decode a counter value previously encoded by encodeCounter().
byte[]	encodeCounter(long value)	Encode a counter value into a byte[] value suitable for use with decodeCounter() and/or adjustCounter().
byte[]	get(byte[] key)	Get the value associated with the given key, if any.
KVPair	getAtLeast(byte[] minKey, byte[] maxKey)	Get the key/value pair having the smallest key greater than or equal to the given minimum, if any.
KVPair	getAtMost(byte[] maxKey, byte[] minKey)	Get the key/value pair having the largest key strictly less than the given maximum, if any.
default CloseableIterator<KVPair>	getRange(byte[] minKey, byte[] maxKey)	Iterate the key/value pairs in the specified range in the forward direction.
CloseableIterator<KVPair>	getRange(byte[] minKey, byte[] maxKey, boolean reverse)	Iterate the key/value pairs in the specified range.
default CloseableIterator<KVPair>	getRange(KeyRange range)	Iterate the key/value pairs in the specified range in the forward direction.
void	put(byte[] key, byte[] value)	Set the value associated with the given key.
void	remove(byte[] key)	Remove the key/value pair with the given key, if it exists.
void	removeRange(byte[] minKey, byte[] maxKey)	Remove all key/value pairs whose keys are in a given range.
default void	removeRange(KeyRange range)	Remove all key/value pairs whose keys are in a given range.

Method Detail

get

byte[] get(byte[] key)

Get the value associated with the given key, if any.

Modifications to the returned byte[] array do not affect this instance.

Parameters:

key - key

Returns:

value associated with key, or null if not found

Throws:

IllegalArgumentException - if key starts with 0xff and such keys are not supported

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

NullPointerException - if key is null

getAtLeast

KVPair getAtLeast(byte[] minKey,
                  byte[] maxKey)

Get the key/value pair having the smallest key greater than or equal to the given minimum, if any.

An optional (exclusive) maximum key may also be specified; if maxKey is null, there is no upper bound; if maxKey <= minKey, null is always returned.

If keys starting with 0xff are not supported by this instance, and minKey starts with 0xff, then this method returns null.

Modifications to the returned byte[] arrays do not affect this instance.

Parameters:

minKey - minimum key (inclusive), or null for no minimum (get the smallest key)

maxKey - maximum key (exclusive), or null for no maximum (no upper bound)

Returns:

smallest key/value pair with key >= minKey and key < maxKey, or null if none exists

Throws:

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

getAtMost

KVPair getAtMost(byte[] maxKey,
                 byte[] minKey)

Get the key/value pair having the largest key strictly less than the given maximum, if any.

An optional (inclusive) minimum key may also be specified; if minKey is null, there is no lower bound (equivalent to a lower bound of the empty byte array); if minKey >= maxKey, null is always returned.

If keys starting with 0xff are not supported by this instance, and maxKey starts with 0xff, then this method behaves as if maxKey were null.

Modifications to the returned byte[] arrays do not affect this instance.

Parameters:

maxKey - maximum key (exclusive), or null for no maximum (get the largest key)

minKey - minimum key (inclusive), or null for no minimum (no lower bound)

Returns:

largest key/value pair with key < maxKey and key >= minKey, or null if none exists

Throws:

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

getRange

CloseableIterator<KVPair> getRange(byte[] minKey,
                                   byte[] maxKey,
                                   boolean reverse)

Iterate the key/value pairs in the specified range. The returned Iterator's remove() method must be supported and should have the same effect as invoking remove() on the corresponding key.

If keys starting with 0xff are not supported by this instance, and minKey starts with 0xff, then this method returns an empty iteration.

If keys starting with 0xff are not supported by this instance, and maxKey starts with 0xff, then this method behaves as if maxKey were null.

The returned Iterator must not throw ConcurrentModificationException; however, whether or not a "live" Iterator reflects any modifications made after its creation is implementation dependent. Implementations that do make post-creation updates visible in the Iterator, even if the update occurs after some delay, must preserve the order in which the modifications actually occurred.

The returned Iterator itself is not guaranteed to be thread safe.

Invokers of this method are encouraged to close() the returned iterators, though this is not required for correct behavior.

Modifications to the returned KVPair key and value byte[] arrays do not affect this instance.

Parameters:

minKey - minimum key (inclusive), or null for no minimum (start at the smallest key)

maxKey - maximum key (exclusive), or null for no maximum (end at the largest key)

reverse - true to return key/value pairs in reverse order (i.e., keys descending)

Returns:

iteration of key/value pairs in the range minKey (inclusive) to maxKey (exclusive)

Throws:

IllegalArgumentException - if minKey > maxKey

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

getRange

default CloseableIterator<KVPair> getRange(byte[] minKey,
                                           byte[] maxKey)

Iterate the key/value pairs in the specified range in the forward direction.

This is a convenience method, equivalent to: getRange(minKey, maxKey, false).

Parameters:

minKey - minimum key (inclusive), or null for no minimum (start at the smallest key)

maxKey - maximum key (exclusive), or null for no maximum (end at the largest key)

Returns:

iteration of key/value pairs in the range minKey (inclusive) to maxKey (exclusive)

Throws:

IllegalArgumentException - if minKey > maxKey

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

getRange

default CloseableIterator<KVPair> getRange(KeyRange range)

Iterate the key/value pairs in the specified range in the forward direction.

This is a convenience method, equivalent to: getRange(range.getMin(), range.getMax(), false).

Parameters:

range - range of keys to iterate

Returns:

iteration of key/value pairs in range

Throws:

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

IllegalArgumentException - if range is null

put

void put(byte[] key,
         byte[] value)

Set the value associated with the given key.

Parameters:

key - key

value - value

Throws:

IllegalArgumentException - if key starts with 0xff and such keys are not supported

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

NullPointerException - if key or value is null

remove

void remove(byte[] key)

Remove the key/value pair with the given key, if it exists.

Parameters:

key - key

Throws:

IllegalArgumentException - if key starts with 0xff and such keys are not supported

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

NullPointerException - if key is null

removeRange

void removeRange(byte[] minKey,
                 byte[] maxKey)

Remove all key/value pairs whose keys are in a given range.

The minKey must be less than or equal to maxKey; if they equal (and not null) then nothing happens; if they are both null then all entries are deleted.

If keys starting with 0xff are not supported by this instance, then:

• If minKey starts with 0xff, then no change occurs
• If maxKey starts with 0xff, then this method behaves as if maxKey were null

Parameters:

minKey - minimum key (inclusive), or null for no minimum

maxKey - maximum key (exclusive), or null for no maximum

Throws:

IllegalArgumentException - if minKey > maxKey

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

removeRange

default void removeRange(KeyRange range)

Remove all key/value pairs whose keys are in a given range.

Equivalent to: removeRange(range.getMin(), range.getMax()).

Parameters:

range - range to remove

Throws:

IllegalArgumentException - if range is null

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

encodeCounter

byte[] encodeCounter(long value)

Encode a counter value into a byte[] value suitable for use with decodeCounter() and/or adjustCounter().

Parameters:

value - desired counter value

Returns:

encoded counter value

Throws:

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

decodeCounter

long decodeCounter(byte[] value)

Decode a counter value previously encoded by encodeCounter().

Parameters:

value - encoded counter value

Returns:

decoded counter value

Throws:

IllegalArgumentException - if value is not a valid counter value

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

NullPointerException - if value is null

adjustCounter

void adjustCounter(byte[] key,
                   long amount)

Adjust the counter at the given key by the given amount.

Ideally this operation should behave in a lock-free manner, so that concurrent transactions can invoke it without conflict. However, when lock-free behavior occurs (if at all) depends on the implementation.

If there is no value associated with key, or key's value is not a valid counter encoding as would be acceptable to decodeCounter(), then how this operation affects key's value is undefined.

Parameters:

key - key

amount - amount to adjust counter value by

Throws:

StaleTransactionException - if an underlying transaction is no longer usable

RetryTransactionException - if an underlying transaction must be retried and is no longer usable

NullPointerException - if key is null

apply

default void apply(Mutations mutations)

Apply all the given Mutations to this instance.

Mutations are always to be applied in this order: removes, puts, counter adjustments.

The implementation in KVStore simply iterates over the individual changes and applies them via remove() (for removals of a single key), removeRange(), put(), and/or adjustCounter(). Implementations that can process batch updates more efficiently are encouraged to override this method.

Parameters:

mutations - mutations to apply

Throws:

IllegalArgumentException - if mutations is null

UnsupportedOperationException - if this instance is immutable