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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/legacy/hacker-guide/bdb.txt | 70 |
1 files changed, 0 insertions, 70 deletions
diff --git a/doc/legacy/hacker-guide/bdb.txt b/doc/legacy/hacker-guide/bdb.txt deleted file mode 100644 index 1a80be813f6..00000000000 --- a/doc/legacy/hacker-guide/bdb.txt +++ /dev/null @@ -1,70 +0,0 @@ - -* How does file translates to key/value pair? ---------------------------------------------- - - in bdb a file is identified by key (obtained by taking basename() of the path of -the file) and file contents are stored as value corresponding to the key in database -file (defaults to glusterfs_storage.db under dirname() directory). - -* symlinks, directories ------------------------ - - symlinks and directories are stored as is. - -* db (database) files ---------------------- - - every directory, including root directory, contains a database file called -glusterfs_storage.db. all the regular files contained in the directory are stored -as key/value pair inside the glusterfs_storage.db. - -* internal data cache ---------------------- - - db does not provide a way to find out the size of the value corresponding to a key. -so, bdb makes DB->get() call for key and takes the length of the value returned. -since DB->get() also returns file contents for key, bdb maintains an internal cache and -stores the file contents in the cache. - every directory maintains a seperate cache. - -* inode number transformation ------------------------------ - - bdb allocates a inode number to each file and directory on its own. bdb maintains a -global counter and increments it after allocating inode number for each file -(regular, symlink or directory). NOTE: bdb does not guarantee persistent inode numbers. - -* checkpoint thread -------------------- - - bdb creates a checkpoint thread at the time of init(). checkpoint thread does a -periodic checkpoint on the DB_ENV. checkpoint is the mechanism, provided by db, to -forcefully commit the logged transactions to the storage. - -NOTES ABOUT FOPS: ------------------ - -lookup() - - 1> do lstat() on the path, if lstat fails, we assume that the file being looked up - is either a regular file or doesn't exist. - 2> lookup in the DB of parent directory for key corresponding to path. if key exists, - return key, with. - NOTE: 'struct stat' stat()ed from DB file is used as a container for 'struct stat' - of the regular file. st_ino, st_size, st_blocks are updated with file's values. - -readv() - - 1> do a lookup in bctx cache. if successful, return the requested data from cache. - 2> if cache missed, do a DB->get() the entire file content and insert to cache. - -writev(): - 1> flush any cached content of this file. - 2> do a DB->put(), with DB_DBT_PARTIAL flag. - NOTE: DB_DBT_PARTIAL is used to do partial update of a value in DB. - -readdir(): - 1> regular readdir() in a loop, and vomit all DB_ENV log files and DB files that - we encounter. - 2> if the readdir() buffer still has space, open a DB cursor and do a sequential - DBC->get() to fill the reaadir buffer. - - |