Class type Nn_blockmap.blockmap_t

class type blockmap_t = object .. end

block maps are in-memory representation of the per-datastore bitmaps whether blocks are used or free. Changes to block maps are done in a transactional way. One can finally get the accumulated updates of a transaction for writing them out to the db

method active : bool

whether this object refers to an existing row in the datastore table. If the object is inactive, the other methods (except id and identity) will fail with Inactive.

method id : int

the datastore db table id

method identity : string

This is the blockmap for this datastore identity

method size : int64

Size of the blockmap in blocks

method n_used : int64

method n_trans : int64

method n_free : int64

Number of used, transitional, free blocks

method fill_blockmap : int64 -> string -> unit

fill_blockmap index data: Fills the blockmap at index with data, a string consisting of 0 and 1. index must be a multiple of 1024. (This is only allowed once per row for init, and is outside any transaction.)

method has_free_blocks : bool

whether there are still free blocks

method reserve : int -> <  > -> int64 list

reserve n owner: finds n free blocks and returns their indices. The reservation is owned by owner, an arbitrary object. Reserved blocks are one of two forms of transitional blocks. Reserved blocks are turned into used blocks at commit time, and freed again on abort.

method free : int64 list -> <  > -> unit

free l owner: deallocates these blocks. If they are still only reserved but not yet committed, they keep their reserved status until commit time, and are freed only then. It is allowed to free kept blocks.

method keep : int64 list -> <  > -> unit

keep l owner: marks these blocks as "to keep" even if a competing transaction frees them. Kept blocks are the other form of transitional blocks. They are counted in n_used as long as there is no committed free. They are counted in n_trans when there is a committed free. In the latter case, the blocks are turned into free blocks at commit or abort time. It is not allowed to keep blocks when there was already a free for them in the same transaction, or a competing transaction could free the block and commit that.

Kept blocks are not entered into the db, so it is not required to get_changes.

method commit : <  > -> unit

commit owner: commits owner's reservations, and makes them permanent. If owner is unknown this is a no-op.

method rollback : <  > -> unit

rollback owner: unreserves owner's blocks. If owner is unknown this is a no-op.

method get_changes : <  > -> (int64 * string) list

get_changes owner: Returns the changes made by owner. This is a list of database rows (start_index,row_data), to be used for SQL UPDATEs. If owner is unknown, the empty list is returned.

method inactivate : unit -> unit

Sets active to false

method dump : string

Get a dump of the internal state

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