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61 строки
2.1 KiB
61 строки
2.1 KiB
File format
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===========
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<beginning_of_file>
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[data block 1]
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[data block 2]
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...
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[data block N]
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[meta block 1]
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...
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[meta block K]
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[metaindex block]
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[index block]
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[Footer] (fixed size; starts at file_size - sizeof(Footer))
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<end_of_file>
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The file contains internal pointers. Each such pointer is called
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a BlockHandle and contains the following information:
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offset: varint64
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size: varint64
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(1) The sequence of key/value pairs in the file are stored in sorted
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order and partitioned into a sequence of data blocks. These blocks
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come one after another at the beginning of the file. Each data block
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is formatted according to the code in block_builder.cc, and then
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optionally compressed.
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(2) After the data blocks we store a bunch of meta blocks. The
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supported meta block types are described below. More meta block types
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may be added in the future. Each meta block is again formatted using
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block_builder.cc and then optionally compressed.
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(3) A "metaindex" block. It contains one entry for every other meta
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block where the key is the name of the meta block and the value is a
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BlockHandle pointing to that meta block.
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(4) An "index" block. This block contains one entry per data block,
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where the key is a string >= last key in that data block and before
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the first key in the successive data block. The value is the
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BlockHandle for the data block.
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(6) At the very end of the file is a fixed length footer that contains
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the BlockHandle of the metaindex and index blocks as well as a magic number.
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metaindex_handle: char[p]; // Block handle for metaindex
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index_handle: char[q]; // Block handle for index
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padding: char[40-p-q]; // 0 bytes to make fixed length
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// (40==2*BlockHandle::kMaxEncodedLength)
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magic: fixed64; // == 0xdb4775248b80fb57
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"stats" Meta Block
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------------------
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This meta block contains a bunch of stats. The key is the name
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of the statistic. The value contains the statistic.
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TODO(postrelease): record following stats.
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data size
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index size
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key size (uncompressed)
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value size (uncompressed)
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number of entries
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number of data blocks
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