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Diffstat (limited to 'doc/legacy/stat-prefetch-design.txt')
| -rw-r--r-- | doc/legacy/stat-prefetch-design.txt | 154 |
1 files changed, 0 insertions, 154 deletions
diff --git a/doc/legacy/stat-prefetch-design.txt b/doc/legacy/stat-prefetch-design.txt deleted file mode 100644 index 68ed423d3dd..00000000000 --- a/doc/legacy/stat-prefetch-design.txt +++ /dev/null @@ -1,154 +0,0 @@ -what is stat-prefetch? -====================== -It is a translator which caches the dentries read in readdir. This dentry -list is stored in the context of fd. Later when lookup happens on -[parent-inode, basename (path)] combination, this list is searched for the -basename. The dentry thus searched is used to fill up the stat corresponding -to path being looked upon, thereby short-cutting lookup calls. This cache is -preserved till closedir is called on the fd. The purpose of this translator -is to optimize operations like 'ls -l', where a readdir is followed by -lookup (stat) calls on each directory entry. - -1. stat-prefetch harnesses the efficiency of short lookup calls - (saves network roundtrip time for lookup calls from being accounted to - the stat call). -2. To maintain the correctness, it does lookup-behind - lookup is winded to - underlying translators after it is unwound to upper translators. - lookup-behind is necessary as inode gets populated in server inode table - only in lookup-cbk and also because various translators store their - contexts in inode contexts during lookup calls. - -fops to be implemented: -======================= -* lookup - 1. check the dentry cache stored in context of fds opened by the same process - on parent inode for basename. If found unwind with cached stat, else wind - the lookup call to underlying translators. - 2. stat is stored in the context of inode if the path being looked upon - happens to be directory. This stat will be used to fill postparent stat - when lookup happens on any of the directory contents. - -* readdir - 1. cache the direntries returned in readdir_cbk in the context of fd. - 2. if the readdir is happening on non-expected offsets (means a seekdir/rewinddir - has happened), cache has to be flushed. - 3. delete the entry corresponding to basename of path on which fd is opened - from cache stored in parent. - -* chmod/fchmod - delete the entry corresponding to basename from cache stored in context of - fds opened on parent inode, since these calls change st_mode and st_ctime of - stat. - -* chown/fchown - delete the entry corresponding to basename from cache stored in context of - fds opened on parent inode, since these calls change st_uid/st_gid and - st_ctime of stat. - -* truncate/ftruncate - delete the entry corresponding to basename from cache stored in context of - fds opened on parent inode, since these calls change st_size/st_mtime of stat. - -* utimens - delete the entry corresponding to basename from cache stored in context of - fds opened on parent inode, since this call changes st_atime/st_mtime of stat. - -* readlink - delete the entry corresponding to basename from cache stored in context of fds - opened on parent inode, since this call changes st_atime of stat. - -* unlink - 1. delete the entry corresponding to basename from cache stored in context of - fds, opened on parent directory containing the file being unlinked. - 2. delete the entry corresponding to basename of parent directory from cache - of grand-parent. - -* rmdir - 1. delete the entry corresponding to basename from cache stored in context of - fds opened on parent inode. - 2. remove the entire cache from all fds opened on inode corresponding to - directory being removed. - 3. delete the entry correspondig to basename of parent from cache stored in - grand-parent. - -* readv - delete the entry corresponding to basename from cache stored in context of fds - opened on parent inode, since readv changes st_atime of file. - -* writev - delete the entry corresponding to basename from cache stored in context of fds - opened on parent inode, since writev can possibly change st_size and definitely - changes st_mtime of file. - -* fsync - there is a confusion here as to whether fsync updates mtime/ctimes. Disk based - filesystems (atleast ext2) just writes the times stored in inode to disk - during fsync and not the time at which fsync is being done. But in glusterfs, - a translator like write-behind actually sends writes during fsync which will - change mtime/ctime. Hence stat-prefetch implements fsync to delete the entry - corresponding to basename from cache stored in context of fds opened on parent - inode. - -* rename - 1. remove entry corresponding to oldname from cache stored in fd contexts of - oldparent. - 2. remove entry corresponding to newname from cache stored in fd contexts of - newparent. - 3. remove entry corresponding to oldparent from cache stored in - old-grand-parent, since removing oldname changes st_mtime and st_ctime - of oldparent stat. - 4. remove entry corresponding to newparent from cache stored in - new-grand-parent, since adding newname changes st_mtime and st_ctime - of newparent stat. - 5. if oldname happens to be a directory, remove entire cache from all fds - opened on it. - -* create/mknod/mkdir/symlink/link - delete entry corresponding to basename of parent directory in which these - operations are happening, from cache stored in context of fds opened on - grand-parent, since adding a new entry to a directory changes st_mtime - and st_ctime of parent directory. - -* setxattr/removexattr - delete the entry corresponding to basename from cache stored in context of - fds opened on parent inode, since setxattr changes st_ctime of file. - -* setdents - 1. remove entry corresponding to basename of path on which fd is opened from - cache stored in context of fds opened on parent. - 2. for each of the entry in the direntry list, delete from cache stored in - context of fd, the entry corresponding to basename of path being passed. - -* getdents - 1. remove entry corresponding to basename of path on which fd is opened from - cache stored in parent, since getdents changes st_atime. - 2. remove entries corresponding to symbolic links from cache, since readlink - would've changed st_atime. - -* checksum - delete the entry corresponding to basename from cache stored in context of - fds opened on parent inode, since st_atime is changed during this call. - -* xattrop/fxattrop - delete the entry corresponding to basename from cache stored in context of fds - opened on parent inode, since these calls modify st_ctime of file. - -callbacks to be implemented: -============================ -* releasedir - free the context stored in fd. - -* forget - dree the stat if the inode corresponds to a directory. - -limitations: -============ -* since a readdir does not return extended attributes of file, if need_xattr is - set, short-cutting of lookup does not happen and lookup is passed to - underlying translators. - -* posix_readdir does not check whether the dentries are spanning across multiple - mount points. Hence it is not transforming inode numbers in stat buffers if - posix is configured to allow export directory spanning on multiple mountpoints. - This is a bug which needs to be fixed. posix_readdir should treat dentries the - same way as if lookup is happening on dentries. |