Module Seqdb_fsys_ao

module Seqdb_fsys_ao: sig .. end

Append-only (ao) filesys variant

These filesys are restricted in so far:

open_file_wr is only permitted with new file names so that a new file must be created.
Furthermore, writing to a file using write_file is only permitted if the file is still the last one.
file_mtime reflects the time of creating the file, not the last modification.
set_file_mtime is forbidden
truncate is forbidden
reserve is a no-op
There are no restrictions for deleting files. Both delete_file and delete_name_from_index work for all files.
rename_file restricts the length of the new name: it is not allowed that the name is so long that a bigger inode must be allocated.

The ao filesystems are special ht filesystems. Because of this, it is possible to implement the ao functions by "plugging in" to Seqdb_fsys_ht. Do this by calling the init function below.

So Seqdb_fsys_ht.ht_base is also used to keep handles for the ao variants. By calling Seqdb_fsys_ht.get_filesys you simply get the ao variant. All the other functions also work, except:

Seqdb_fsys_ht.create_filesys cannot create the ao variant. Use the create_ao_filesys function below instead.
Seqdb_fsys_ht.get_iterator works, but iteration starts always at the beginning. Use get_ao_iterator below for starting at any mtime.
Seqdb_fsys_ht.get_idx_iterator works, but iteration starts always at the beginning. There is no ao counterpart with more possibilities.

type ao_params = {

ao_time_mark_period : int; (* TIMEMP in seconds *)

}

Additional parameters for the ao variant of file systems

exception Append_only_restriction of string

Raised if one of the mentioned restrictions would have been violated. The string argument is the path to the filesystem

val init : unit -> unit

Initialize Seqdb_fsys_ht in a special way so the ao variant is known there

val create_ao_filesys : Seqdb_fsys_ht.ht_base ->
       string ->
       Seqdb_fsys_ht.params ->
       ao_params ->
       Seqdb_fsys_ht.ht_file_descr Seqdb_fsys_types.file_system

Create an ao file system

val filesys_ao_params : Seqdb_fsys_ht.ht_base -> string -> ao_params

Get the special ao parameters

val configure_ao_filesys : ?read_only_mode:bool -> Seqdb_fsys_ht.ht_base -> string -> unit

- read_only_mode: If true, the fsys can only be read - writes will fail. The advantage is that the fsys lock can be quicker released.

val get_ao_iterator : ?at_mtime:int64 ->
       Seqdb_fsys_ht.ht_base ->
       string -> Seqdb_fsys_ht.ht_file_descr Seqdb_fsys_types.file_system_iterator

Starts iterating at the first file whose mtime is greater or equal to at_mtime (or the beginning of the filesys if at_mtime is omitted).