reverting disastrous MOE commit, returning to r21

git-svn-id: https://leveldb.googlecode.com/svn/trunk@23 62dab493-f737-651d-591e-8d6aee1b9529

1 files changed, 61 insertions, 0 deletions

diff --git a/doc/table_format.txt b/doc/table_format.txt
new file mode 100644
index 0000000..ad5aa4b
--- /dev/null
+++ b/doc/table_format.txt
@@ -0,0 +1,61 @@
+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
+
+(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]; // 0 bytes to make fixed length
+       			 	       // (40==2*BlockHandle::kMaxEncodedLength)
+       magic:		       fixed64;    // == 0xdb4775248b80fb57
+
+"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