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State: added a function to populate the predecessors storage

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Marco Stronati 2018-01-25 11:25:50 +01:00 committed by Benjamin Canou
parent eaf2103967
commit 738310df62
1 changed files with 46 additions and 2 deletions
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48
src/lib_shell/state.ml
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@ -144,6 +144,48 @@ let rec predecessor (store : Store.Block.store) (b: Block_hash.t) n =
predecessor store pred (n-1)
end
(** The number of predecessors stored per block.
This value chosen to compute efficiently block locators that
can cover a chain of 2 months, at 1 block/min, which is ~86K
blocks at the cost in space of ~72MB.
|locator| = log2(|chain|/10) -1
*)
let stored_predecessors_size = 12
(**
Takes a block and populates its predecessors store, under the
assumption that all its predecessors have their store already
populated. The precedecessors are distributed along the chain, up
to the genesis, at a distance from [b] that grows exponentially.
The store tabulates a function [p] from distances to block_ids such
that if [p(b,d)=b'] then [b'] is at distance 2^d from [b].
Example of how previous predecessors are used:
p(n,0) = n-1
p(n,1) = n-2 = p(n-1,0)
p(n,2) = n-4 = p(n-2,1)
p(n,3) = n-8 = p(n-4,2)
p(n,4) = n-16 = p(n-8,3)
*)
let store_predecessors (store: Store.Block.store) (b: Block_hash.t) : unit Lwt.t =
let rec loop pred dist =
if dist = stored_predecessors_size
then Lwt.return_unit
else
Store.Block.Predecessors.read_opt (store, pred) (dist-1) >>= function
| None -> Lwt.return_unit (* we reached genesis *)
| Some p ->
Store.Block.Predecessors.store (store, b) dist p >>= fun () ->
loop p (dist+1)
in
(* the first predecessor is fetched from the header *)
Store.Block.Contents.read_exn (store, b) >>= fun contents ->
let pred = contents.header.shell.predecessor in
if Block_hash.equal b pred then
Lwt.return_unit (* genesis *)
else
Store.Block.Predecessors.store (store,b) 0 pred >>= fun () ->
loop pred 1
let compute_locator_from_hash (net : net_state) ?(size = 200) head =
Shared.use net.block_store begin fun block_store ->
Store.Block.Contents.read_exn (block_store, head) >>= fun { header } ->
@ -161,7 +203,7 @@ module Locked_block = struct
let shell : Block_header.shell_header = {
level = 0l ;
proto_level = 0 ;
predecessor = genesis.block ;
predecessor = genesis.block ; (* genesis' predecessor is genesis *)
timestamp = genesis.time ;
fitness = [] ;
validation_passes = 0 ;
@ -447,7 +489,7 @@ module Block = struct
let predecessor { net_state ; contents = { header } ; hash } =
if Block_hash.equal hash header.shell.predecessor then
Lwt.return_none
Lwt.return_none (* we are at genesis *)
else
read_exn net_state header.shell.predecessor >>= fun block ->
Lwt.return (Some block)
@ -507,6 +549,8 @@ module Block = struct
Lwt_list.iteri_p
(fun i ops -> Store.Block.Operations.store (store, hash) i ops)
operations >>= fun () ->
(* Store predecessors *)
store_predecessors store hash >>= fun () ->
(* Update the chain state. *)
Shared.use net_state.chain_state begin fun chain_state ->
let store = chain_state.chain_store in