Overview The WriteBatch class holds a collection of updates to apply atomically to a database. All updates are applied in the order they are added to the WriteBatch. WriteBatch supports Put, Delete, Merge, and DeleteRange operations.
Constructor explicit WriteBatch ( size_t reserved_bytes = 0 , size_t max_bytes = 0 ) explicit WriteBatch ( size_t reserved_bytes, size_t max_bytes, size_t protection_bytes_per_key, size_t default_cf_ts_sz) explicit WriteBatch ( const std ::string & rep) explicit WriteBatch ( std ::string && rep)
Number of bytes to pre-allocate for the batch. Useful for avoiding reallocations when batch size is known.
Maximum size of the batch in bytes. If 0, no limit is enforced.
Number of bytes used to store protection information for each key entry. Currently supported values are zero (disabled) and eight.
Write Operations Put Store the mapping “key->value” in the database.
Status Put ( ColumnFamilyHandle * column_family , const Slice & key , const Slice & value ) Status Put ( const Slice & key , const Slice & value ) Status Put ( ColumnFamilyHandle * column_family , const Slice & key , const Slice & ts , const Slice & value ) Status Put ( ColumnFamilyHandle * column_family , const SliceParts & key , const SliceParts & value )
Target column family. If nullptr, uses the default column family.
The key to store. When user-defined timestamp is enabled, key should point to a contiguous buffer with timestamp appended after user key.
User-defined timestamp for the key.
The value to associate with the key.
TimedPut (Experimental) Stores the mapping “key->value” with a specified write time.
Status TimedPut ( ColumnFamilyHandle * column_family , const Slice & key , const Slice & value , uint64_t write_unix_time )
Unix timestamp indicating when the write occurred.
PutEntity Store wide column entities.
Status PutEntity ( ColumnFamilyHandle * column_family , const Slice & key , const WideColumns & columns ) Status PutEntity ( const Slice & key , const AttributeGroups & attribute_groups )
Delete Erase a key from the database.
Status Delete ( ColumnFamilyHandle * column_family , const Slice & key ) Status Delete ( const Slice & key ) Status Delete ( ColumnFamilyHandle * column_family , const Slice & key , const Slice & ts ) Status Delete ( ColumnFamilyHandle * column_family , const SliceParts & key )
SingleDelete See DB::SingleDelete() for semantics and constraints.
Status SingleDelete ( ColumnFamilyHandle * column_family , const Slice & key ) Status SingleDelete ( const Slice & key ) Status SingleDelete ( ColumnFamilyHandle * column_family , const Slice & key , const Slice & ts )
DeleteRange Delete a range of keys [begin_key, end_key).
Status DeleteRange ( ColumnFamilyHandle * column_family , const Slice & begin_key , const Slice & end_key ) Status DeleteRange ( const Slice & begin_key , const Slice & end_key ) Status DeleteRange ( ColumnFamilyHandle * column_family , const Slice & begin_key , const Slice & end_key , const Slice & ts )
Start of the range (inclusive).
End of the range (exclusive).
Merge Merge “value” with the existing value of “key” using the merge operator.
Status Merge ( ColumnFamilyHandle * column_family , const Slice & key , const Slice & value ) Status Merge ( const Slice & key , const Slice & value )
Utility Methods Clear Clear all updates buffered in this batch. Internally calls resize() on the string buffer, so allocated memory capacity may not be freed.
Count Returns the number of updates in the batch.
GetDataSize size_t GetDataSize () const
Returns the size of the serialized batch in bytes.
Data const std :: string & Data () const
Retrieve the serialized version of this batch.
SetMaxBytes void SetMaxBytes ( size_t max_bytes )
Set the maximum size limit for the batch.
Save Points Save points allow you to rollback portions of a WriteBatch.
SetSavePoint Records the state of the batch for future calls to RollbackToSavePoint(). May be called multiple times.
RollbackToSavePoint Status RollbackToSavePoint ()
Remove all entries added since the most recent SetSavePoint() and removes that save point. Returns Status::NotFound() if no save point exists.
PopSavePoint Pop the most recent save point without rolling back. Returns Status::NotFound() if no save point exists.
Content Queries Query what types of operations are in the batch:
bool HasPut () const bool HasTimedPut () const bool HasPutEntity () const bool HasDelete () const bool HasSingleDelete () const bool HasDeleteRange () const bool HasMerge () const bool HasBeginPrepare () const bool HasEndPrepare () const bool HasCommit () const bool HasRollback () const
Iteration Handler Implement a WriteBatch::Handler to iterate over the contents of a batch:
class Handler { public: virtual Status PutCF ( uint32_t column_family_id , const Slice & key , const Slice & value ); virtual Status DeleteCF ( uint32_t column_family_id , const Slice & key ); virtual Status SingleDeleteCF ( uint32_t column_family_id , const Slice & key ); virtual Status DeleteRangeCF ( uint32_t column_family_id , const Slice & begin_key , const Slice & end_key ); virtual Status MergeCF ( uint32_t column_family_id , const Slice & key , const Slice & value ); virtual void LogData ( const Slice & blob ); virtual bool Continue (); };
Iterate Status Iterate ( Handler * handler ) const
Iterate over the batch contents, calling the appropriate handler methods.
Examples Basic Usage
Update Order
Save Points
Multi-Column Family
Iterating a Batch
// Atomically apply a set of updates WriteBatch batch; batch . Delete ( "key1" ); batch . Put ( "key2" , "value2" ); batch . Put ( "key3" , "value3" ); Status s = db -> Write ( WriteOptions (), & batch); assert ( s . ok ());
Thread Safety Multiple threads can invoke const methods on a WriteBatch without external synchronization. However, if any thread may call a non-const method, all threads accessing the same WriteBatch must use external synchronization.
See Also