gitty_driver_files.pl -- Gitty plain files driver

This version of the driver uses plain files to store the gitty data. It consists of a nested directory structure with files named after the hash. Objects and hash computation is the same as for git. The heads (files) are computed on startup by scanning all objects. There is a file ref/head that is updated if a head is updated. Other clients can watch this file and update their notion of the head. This implies that the store can handle multiple clients that can access a shared file system, optionally shared using NFS from different machines.

The store is simple and robust. The main disadvantages are long startup times as the store holds more objects and relatively high disk usage due to rounding the small objects to disk allocation units.

bug: - Shared access does not work on Windows.

gitty_close(+Store) is det

Close resources associated with a store.

gitty_file(+Store, ?File, ?Ext, ?Head) is nondet

True when File entry in the gitty store and Head is the HEAD revision.

load_plain_commit(+Store, +Hash, -Meta:dict) is semidet

Load the commit data as a dict. Loaded commits are cached in commit/3. Note that only adding a fact to the cache is synchronized. This means that during a race situation we may load the same object multiple times from disk, but this is harmless while a lock around the whole predicate serializes loading different objects, which is not needed.

store_object(+Store, +Hash, +Header:string, +Data:string) is det

Store the actual object. The store must associate Hash with the concatenation of Hdr and Data.

load_object(+Store, +Hash, -Data, -Type, -Size) is det

Load the given object.

load_object_header(+Store, +Hash, -Type, -Size) is det[private]

Load the header of an object

gitty_rescan(?Store) is det

Update our view of the shared storage for all stores matching Store.

gitty_scan(+Store) is det[private]

Scan gitty store for files (entries), filling head/3. This is performed lazily at first access to the store.

@tdb Possibly we need to maintain a cached version of this index to avoid having to open all objects of the gitty store.

read_heads_from_objects(+Store) is det[private]

Establish the head(Store,File,Ext,Hash) relation by reading all objects and adding a fact for the most recent commit.

gitty_scan_latest(+Store)[private]

Scans the gitty store, extracting the latest version of each named entry.

gitty_hash(+Store, ?Hash) is nondet

True when Hash is an object in the store.

delete_object(+Store, +Hash)

Delete an existing object

gitty_object_file(+Store, +Hash, -Path) is det

True when Path is the file at which the object with Hash is stored.

gitty_update_head(+Store, +Name, +OldCommit, +NewCommit) is det

Update the head of a gitty store for Name. OldCommit is the current head and NewCommit is the new head. If Name is created, and thus there is no head, OldCommit must be -.

This operation can fail because another writer has updated the head. This can both be in-process or another process.

remote_updates(+Store)[private]

Watch for remote updates to the store. We only do this if we did not do so the last second.

remote_updates(+Store, -List) is det[private]

Find updates from other gitties on the same filesystem. Note that we have to push/pop the input context to avoid creating a notion of an input context which possibly relate messages incorrectly to the sync file.

restore_heads_from_remote(Store)[private]

Restore the known heads by reading the remote sync file.

delete_head(+Store, +Head) is det

Delete Head from Store. Used by gitty_fsck/1 to remove heads that have no commits. Should we forward this to remotes, or should they do their own thing?

set_head(+Store, +File, +Hash) is det

Set the head of the given File to Hash

repack_objects(+Store, +Options) is det[multifile]

Repack objects of Store for reduced disk usage and enhanced performance. By default this picks up all file objects of the store and all existing small pack files. Options:

small_pack(+Bytes): Consider all packs with less than Bytes as small and repack them. Default 10Mb
min_files(+Count): Do not repack if there are less than Count new files. Default 1,000.

pack_objects(+Store, +Objects, +Packs, +PackDir, -PackFile, +Options) is det