Database interactions ********************* Database object =============== .. py:class:: rocksdb.DB .. py:method:: __init__(db_name, Options opts, read_only=False) :param unicode db_name: Name of the database to open :param opts: Options for this specific database :type opts: :py:class:`rocksdb.Options` :param bool read_only: If ``True`` the database is opened read-only. All DB calls which modify data will raise an Exception. .. py:method:: put(key, value, sync=False, disable_wal=False, ignore_missing_column_families=False, no_slowdown=False, low_pri=False) Set the database entry for "key" to "value". :param bytes key: Name for this entry :param bytes value: Data for this entry :param bool sync: If ``True``, the write will be flushed from the operating system buffer cache (by calling WritableFile::Sync()) before the write is considered complete. If this flag is true, writes will be slower. If this flag is ``False``, and the machine crashes, some recent writes may be lost. Note that if it is just the process that crashes (i.e., the machine does not reboot), no writes will be lost even if ``sync == False``. In other words, a DB write with ``sync == False`` has similar crash semantics as the "write()" system call. A DB write with ``sync == True`` has similar crash semantics to a "write()" system call followed by "fdatasync()". :param bool disable_wal: If ``True``, writes will not first go to the write ahead log, and the write may got lost after a crash. :param bool ignore_missing_column_families: If ``True`` and if user is trying to write to column families that don't exist (they were dropped), ignore the write (don't return an error). If there are multiple writes in a WriteBatch, other writes will succeed. :param bool no_slowdown: If ``True`` and we need to wait or sleep for the write request, fails immediately with Status::Incomplete(). :param bool low_pri: If ``True``, this write request is of lower priority if compaction is behind. In this case, no_slowdown = true, the request will be cancelled immediately with Status::Incomplete() returned. Otherwise, it will be slowed down. The slowdown value is determined by RocksDB to guarantee it introduces minimum impacts to high priority writes. .. py:method:: delete(key, sync=False, disable_wal=False, ignore_missing_column_families=False, no_slowdown=False, low_pri=False) Remove the database entry for "key". :param bytes key: Name to delete :param sync: See :py:meth:`rocksdb.DB.put` :param disable_wal: See :py:meth:`rocksdb.DB.put` :param ignore_missing_column_families: See :py:meth:`rocksdb.DB.put` :param no_slowdown: See :py:meth:`rocksdb.DB.put` :param low_pri: See :py:meth:`rocksdb.DB.put` :raises rocksdb.errors.NotFound: If the key did not exists .. py:method:: merge(key, value, sync=False, disable_wal=False, ignore_missing_column_families=False, no_slowdown=False, low_pri=False) Merge the database entry for "key" with "value". The semantics of this operation is determined by the user provided merge_operator when opening DB. See :py:meth:`rocksdb.DB.put` for the parameters :raises: :py:exc:`rocksdb.errors.NotSupported` if this is called and no :py:attr:`rocksdb.Options.merge_operator` was set at creation .. py:method:: write(batch, sync=False, disable_wal=False, ignore_missing_column_families=False, no_slowdown=False, low_pri=False) Apply the specified updates to the database. :param rocksdb.WriteBatch batch: Batch to apply :param sync: See :py:meth:`rocksdb.DB.put` :param disable_wal: See :py:meth:`rocksdb.DB.put` :param ignore_missing_column_families: See :py:meth:`rocksdb.DB.put` :param no_slowdown: See :py:meth:`rocksdb.DB.put` :param low_pri: See :py:meth:`rocksdb.DB.put` .. py:method:: get(key, verify_checksums=False, fill_cache=True, snapshot=None, read_tier="all") :param bytes key: Name to get :param bool verify_checksums: If ``True``, all data read from underlying storage will be verified against corresponding checksums. :param bool fill_cache: Should the "data block", "index block" or "filter block" read for this iteration be cached in memory? Callers may wish to set this field to ``False`` for bulk scans. :param snapshot: If not ``None``, read as of the supplied snapshot (which must belong to the DB that is being read and which must not have been released). Is it ``None`` a implicit snapshot of the state at the beginning of this read operation is used :type snapshot: :py:class:`rocksdb.Snapshot` :param string read_tier: Specify if this read request should process data that ALREADY resides on a particular cache. If the required data is not found at the specified cache, then :py:exc:`rocksdb.errors.Incomplete` is raised. | Use ``all`` if a fetch from disk is allowed. | Use ``cache`` if only data from cache is allowed. :returns: ``None`` if not found, else the value for this key .. py:method:: multi_get(keys, verify_checksums=False, fill_cache=True, snapshot=None, read_tier="all") :param keys: Keys to fetch :type keys: list of bytes For the other params see :py:meth:`rocksdb.DB.get` :returns: A ``dict`` where the value is either ``bytes`` or ``None`` if not found :raises: If the fetch for a single key fails .. note:: keys will not be "de-duplicated". Duplicate keys will return duplicate values in order. .. py:method:: key_may_exist(key, fetch=False, verify_checksums=False, fill_cache=True, snapshot=None, read_tier="all") If the key definitely does not exist in the database, then this method returns ``False``, else ``True``. If the caller wants to obtain value when the key is found in memory, fetch should be set to ``True``. This check is potentially lighter-weight than invoking DB::get(). One way to make this lighter weight is to avoid doing any IOs. :param bytes key: Key to check :param bool fetch: Obtain also the value if found For the other params see :py:meth:`rocksdb.DB.get` :returns: * ``(True, None)`` if key is found but value not in memory * ``(True, None)`` if key is found and ``fetch=False`` * ``(True, )`` if key is found and value in memory and ``fetch=True`` * ``(False, None)`` if key is not found .. py:method:: iterkeys(verify_checksums=False, fill_cache=True, snapshot=None, read_tier="all") Iterate over the keys For other params see :py:meth:`rocksdb.DB.get` :returns: A iterator object which is not valid yet. Call first one of the seek methods of the iterator to position it :rtype: :py:class:`rocksdb.BaseIterator` .. py:method:: itervalues(verify_checksums=False, fill_cache=True, snapshot=None, read_tier="all") Iterate over the values For other params see :py:meth:`rocksdb.DB.get` :returns: A iterator object which is not valid yet. Call first one of the seek methods of the iterator to position it :rtype: :py:class:`rocksdb.BaseIterator` .. py:method:: iteritems(verify_checksums=False, fill_cache=True, snapshot=None, read_tier="all") Iterate over the items For other params see :py:meth:`rocksdb.DB.get` :returns: A iterator object which is not valid yet. Call first one of the seek methods of the iterator to position it :rtype: :py:class:`rocksdb.BaseIterator` .. py:method:: snapshot() Return a handle to the current DB state. Iterators created with this handle will all observe a stable snapshot of the current DB state. :rtype: :py:class:`rocksdb.Snapshot` .. py:method:: get_property(prop) DB implementations can export properties about their state via this method. If "property" is a valid property understood by this DB implementation, a byte string with its value is returned. Otherwise ``None`` Valid property names include: * ``b"rocksdb.num-files-at-level"``: return the number of files at level , where is an ASCII representation of a level number (e.g. "0"). * ``b"rocksdb.stats"``: returns a multi-line byte string that describes statistics about the internal operation of the DB. * ``b"rocksdb.sstables"``: returns a multi-line byte string that describes all of the sstables that make up the db contents. * ``b"rocksdb.num-immutable-mem-table"``: Number of immutable mem tables. * ``b"rocksdb.mem-table-flush-pending"``: Returns ``1`` if mem table flush is pending, otherwise ``0``. * ``b"rocksdb.compaction-pending"``: Returns ``1`` if a compaction is pending, otherweise ``0``. * ``b"rocksdb.background-errors"``: Returns accumulated background errors encountered. * ``b"rocksdb.cur-size-active-mem-table"``: Returns current size of the active memtable. .. py:method:: get_live_files_metadata() Returns a list of all table files. It returns a list of dict's were each dict has the following keys. ``name`` Name of the file ``level`` Level at which this file resides ``size`` File size in bytes ``smallestkey`` Smallest user defined key in the file ``largestkey`` Largest user defined key in the file ``smallest_seqno`` smallest seqno in file ``largest_seqno`` largest seqno in file .. py:method:: compact_range(begin=None, end=None, ** options) Compact the underlying storage for the key range [begin,end]. The actual compaction interval might be superset of [begin, end]. In particular, deleted and overwritten versions are discarded, and the data is rearranged to reduce the cost of operations needed to access the data. This operation should typically only be invoked by users who understand the underlying implementation. ``begin == None`` is treated as a key before all keys in the database. ``end == None`` is treated as a key after all keys in the database. Therefore the following call will compact the entire database: ``db.compact_range()``. Note that after the entire database is compacted, all data are pushed down to the last level containing any data. If the total data size after compaction is reduced, that level might not be appropriate for hosting all the files. In this case, client could set change_level to ``True``, to move the files back to the minimum level capable of holding the data set or a given level (specified by non-negative target_level). :param bytes begin: Key where to start compaction. If ``None`` start at the beginning of the database. :param bytes end: Key where to end compaction. If ``None`` end at the last key of the database. :param bool change_level: If ``True``, compacted files will be moved to the minimum level capable of holding the data or given level (specified by non-negative target_level). If ``False`` you may end with a bigger level than configured. Default is ``False``. :param int target_level: If change_level is true and target_level have non-negative value, compacted files will be moved to target_level. Default is ``-1``. :param string bottommost_level_compaction: For level based compaction, we can configure if we want to skip/force bottommost level compaction. By default level based compaction will only compact the bottommost level if there is a compaction filter. It can be set to the following values. ``skip`` Skip bottommost level compaction ``if_compaction_filter`` Only compact bottommost level if there is a compaction filter. This is the default. ``force`` Always compact bottommost level .. py:attribute:: options Returns the associated :py:class:`rocksdb.Options` instance. .. note:: Changes to this object have no effect anymore. Consider this as read-only Iterator ======== .. py:class:: rocksdb.BaseIterator Base class for all iterators in this module. After creation a iterator is invalid. Call one of the seek methods first before starting iteration .. py:method:: seek_to_first() Position at the first key in the source .. py:method:: seek_to_last() Position at the last key in the source .. py:method:: seek(key) :param bytes key: Position at the first key in the source that at or past Methods to support the python iterator protocol .. py:method:: __iter__() .. py:method:: __next__() .. py:method:: __reversed__() Snapshot ======== .. py:class:: rocksdb.Snapshot Opaque handler for a single Snapshot. Snapshot is released if nobody holds a reference on it. Retrieved via :py:meth:`rocksdb.DB.snapshot` WriteBatch ========== .. py:class:: rocksdb.WriteBatch WriteBatch holds a collection of updates to apply atomically to a DB. The updates are applied in the order in which they are added to the WriteBatch. For example, the value of "key" will be "v3" after the following batch is written:: batch = rocksdb.WriteBatch() batch.put(b"key", b"v1") batch.delete(b"key") batch.put(b"key", b"v2") batch.put(b"key", b"v3") .. py:method:: __init__(data=None) Creates a WriteBatch. :param bytes data: A serialized version of a previous WriteBatch. As retrieved from a previous .data() call. If ``None`` a empty WriteBatch is generated .. py:method:: put(key, value) Store the mapping "key->value" in the database. :param bytes key: Name of the entry to store :param bytes value: Data of this entry .. py:method:: merge(key, value) Merge "value" with the existing value of "key" in the database. :param bytes key: Name of the entry to merge :param bytes value: Data to merge .. py:method:: delete(key) If the database contains a mapping for "key", erase it. Else do nothing. :param bytes key: Key to erase .. py:method:: clear() Clear all updates buffered in this batch. .. note:: Don't call this method if there is an outstanding iterator. Calling :py:meth:`rocksdb.WriteBatch.clear()` with outstanding iterator, leads to SEGFAULT. .. py:method:: data() Retrieve the serialized version of this batch. :rtype: ``bytes`` .. py:method:: count() Returns the number of updates in the batch :rtype: int .. py:method:: __iter__() Returns an iterator over the current contents of the write batch. If you add new items to the batch, they are not visible for this iterator. Create a new one if you need to see them. .. note:: Calling :py:meth:`rocksdb.WriteBatch.clear()` on the write batch invalidates the iterator. Using a iterator where its corresponding write batch has been cleared, leads to SEGFAULT. :rtype: :py:class:`rocksdb.WriteBatchIterator` WriteBatchIterator ================== .. py:class:: rocksdb.WriteBatchIterator .. py:method:: __iter__() Returns self. .. py:method:: __next__() Returns the next item inside the corresponding write batch. The return value is a tuple of always size three. First item (Name of the operation): * ``"Put"`` * ``"Merge"`` * ``"Delete"`` Second item (key): Key for this operation. Third item (value): The value for this operation. Empty for ``"Delete"``. Repair DB ========= .. py:function:: repair_db(db_name, opts) :param unicode db_name: Name of the database to open :param opts: Options for this specific database :type opts: :py:class:`rocksdb.Options` If a DB cannot be opened, you may attempt to call this method to resurrect as much of the contents of the database as possible. Some data may be lost, so be careful when calling this function on a database that contains important information. Errors ====== .. py:exception:: rocksdb.errors.NotFound .. py:exception:: rocksdb.errors.Corruption .. py:exception:: rocksdb.errors.NotSupported .. py:exception:: rocksdb.errors.InvalidArgument .. py:exception:: rocksdb.errors.RocksIOError .. py:exception:: rocksdb.errors.MergeInProgress .. py:exception:: rocksdb.errors.Incomplete