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Diffstat (limited to 'src/leveldb/doc/table_format.txt')
| -rw-r--r-- | src/leveldb/doc/table_format.txt | 104 |
1 files changed, 0 insertions, 104 deletions
diff --git a/src/leveldb/doc/table_format.txt b/src/leveldb/doc/table_format.txt deleted file mode 100644 index ca8f9b4460..0000000000 --- a/src/leveldb/doc/table_format.txt +++ /dev/null @@ -1,104 +0,0 @@ -File format -=========== - - <beginning_of_file> - [data block 1] - [data block 2] - ... - [data block N] - [meta block 1] - ... - [meta block K] - [metaindex block] - [index block] - [Footer] (fixed size; starts at file_size - sizeof(Footer)) - <end_of_file> - -The file contains internal pointers. Each such pointer is called -a BlockHandle and contains the following information: - offset: varint64 - size: varint64 -See https://developers.google.com/protocol-buffers/docs/encoding#varints -for an explanation of varint64 format. - -(1) The sequence of key/value pairs in the file are stored in sorted -order and partitioned into a sequence of data blocks. These blocks -come one after another at the beginning of the file. Each data block -is formatted according to the code in block_builder.cc, and then -optionally compressed. - -(2) After the data blocks we store a bunch of meta blocks. The -supported meta block types are described below. More meta block types -may be added in the future. Each meta block is again formatted using -block_builder.cc and then optionally compressed. - -(3) A "metaindex" block. It contains one entry for every other meta -block where the key is the name of the meta block and the value is a -BlockHandle pointing to that meta block. - -(4) An "index" block. This block contains one entry per data block, -where the key is a string >= last key in that data block and before -the first key in the successive data block. The value is the -BlockHandle for the data block. - -(6) At the very end of the file is a fixed length footer that contains -the BlockHandle of the metaindex and index blocks as well as a magic number. - metaindex_handle: char[p]; // Block handle for metaindex - index_handle: char[q]; // Block handle for index - padding: char[40-p-q]; // zeroed bytes to make fixed length - // (40==2*BlockHandle::kMaxEncodedLength) - magic: fixed64; // == 0xdb4775248b80fb57 (little-endian) - -"filter" Meta Block -------------------- - -If a "FilterPolicy" was specified when the database was opened, a -filter block is stored in each table. The "metaindex" block contains -an entry that maps from "filter.<N>" to the BlockHandle for the filter -block where "<N>" is the string returned by the filter policy's -"Name()" method. - -The filter block stores a sequence of filters, where filter i contains -the output of FilterPolicy::CreateFilter() on all keys that are stored -in a block whose file offset falls within the range - - [ i*base ... (i+1)*base-1 ] - -Currently, "base" is 2KB. So for example, if blocks X and Y start in -the range [ 0KB .. 2KB-1 ], all of the keys in X and Y will be -converted to a filter by calling FilterPolicy::CreateFilter(), and the -resulting filter will be stored as the first filter in the filter -block. - -The filter block is formatted as follows: - - [filter 0] - [filter 1] - [filter 2] - ... - [filter N-1] - - [offset of filter 0] : 4 bytes - [offset of filter 1] : 4 bytes - [offset of filter 2] : 4 bytes - ... - [offset of filter N-1] : 4 bytes - - [offset of beginning of offset array] : 4 bytes - lg(base) : 1 byte - -The offset array at the end of the filter block allows efficient -mapping from a data block offset to the corresponding filter. - -"stats" Meta Block ------------------- - -This meta block contains a bunch of stats. The key is the name -of the statistic. The value contains the statistic. -TODO(postrelease): record following stats. - data size - index size - key size (uncompressed) - value size (uncompressed) - number of entries - number of data blocks |