Added an article about LevelDB (#220)

docs/leveldb_format.md

@@ -0,0 +1,52 @@
+---
+tags:
+  - Database
+  - File Formats
+---
+
+LevelDB is an Open Source key-value store database format.
+
+The LevelDB database format is used to store various kinds of application-level
+information such as the [Google Chrome](google_chrome.md) local storage.
+
+A LevelDB database consists of a directory that contains the following files:
+
+* `[0-9]{6}.ldb` (sorted tables file)
+* `[0-9]{6}.log` (write ahead log file)
+* CURRENT (contains the name of the current MANIFEST file)
+* LOCK
+* LOG, LOG.old (log with informational messages)
+* MANIFEST-000001 (information about the sorted tables that make up the database)
+
+## MIME types
+
+Currently there are no know mime type for the LevelDB formats .
+
+## File signature
+
+Only sorted tables files are known to have an unique signature
+"\x57\xfb\x80\x8b\x24\x75\x47\xdb" in the last 8 bytes of the file.
+
+## File types
+
+LevelDB is known to use several different file formats
+
+* log descriptor format, used by MANIFEST-000001
+* log format, used by `[0-9]{6}.log`
+* table format, used by `[0-9]{6}.ldb`
+* text, used by CURRENT, LOG, LOG.old
+
+## External Links
+
+* [LevelDB: Files](https://github.com/google/leveldb/blob/main/doc/impl.md)
+* [LevelDB: leveldb File format](https://github.com/google/leveldb/blob/main/doc/table_format.md)
+* [LevelDB: leveldb Log format](https://github.com/google/leveldb/blob/main/doc/log_format.md)
+* [Wikipedia: LevelDB](https://en.wikipedia.org/wiki/LevelDB)
+* [Recovering Deleted Data from LevelDB](https://antimatter15.com/2015/12/recovering-deleted-data-from-leveldb/),
+  by Kevin Kwok, December 2, 2015
+
+### IndexedDB
+
+* [Chromium - LevelDB Coding Scheme](https://github.com/chromium/chromium/blob/master/content/browser/indexed_db/docs/leveldb_coding_scheme.md)
+* [How the browsers store IndexedDB data](https://www.aaron-powell.com/posts/2012-10-05-indexeddb-storage/),
+  by Aaron Powell, October 5, 2012