Add more db documentation.

1 files changed, 37 insertions, 1 deletions

diff --git a/doc/db.md b/doc/db.md
index 79ff9ac..7a411d1 100644
--- a/doc/db.md
+++ b/doc/db.md
@@ -17,7 +17,39 @@ Data entries are stored together with three attributes:
 - leaf hash
 
   hash over specific parts of the entry, usually together with a
-  timestamp, for use in a merkle tree
+  timestamp for use in a merkle tree
+
+## Storage in a file system
+
+Two files (catlfish names in parentheses):
+
+- treesize (treesize)
+
+  filename is static, contains one line -- the number of entries in
+  the database
+
+- index (index)
+
+  filename is static, contains one line per entry -- the leafhash
+
+Three directories, "bucketed" in three levels, one file per database
+entry:
+
+- entry (certentries)
+
+  filename=leafhash, content=the actual data of the entry
+
+- entryhash (entryhash)
+
+  filename=entryhash, content=leafhash
+
+- indexforhash (certindex)
+
+  filename=leafhash, content=index
+
+## Distributed
+
+TODO: describe distribution
 
 ## Erlang code in src/
 
@@ -31,6 +63,10 @@ Data entries are stored together with three attributes:
   file-based storage for ordered append-only lists of fixed-sized
   entries, retrievable by index
 
+- perm.erl
+
+  reading and writing of files
+
 - atomic.erl
 
   atomic file operations