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Add option description

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Add documentation of new options
This commit is contained in:
Martin Sumner 2017-11-07 10:22:27 +00:00
parent f358bd7622
commit 0af0d85239
1 changed files with 21 additions and 6 deletions
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27
src/leveled_bookie.erl
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@ -145,19 +145,34 @@ book_start(RootPath, LedgerCacheSize, JournalSize, SyncStrategy) ->
%% @doc Start a Leveled Key/Value store - full options support.
%%
%% Allows an options proplists to be passed for setting options. There are
%% two primary additional options this allows over book_start/4:
%% four primary additional options this allows over book_start/4:
%% - retain_strategy
%% - waste_retention_period
%% - compression_method
%% - compression_point
%%
%% Both of these relate to compaction in the Journal. The retain_strategy
%% determines if a skinny record of the object should be retained following
%% compaction, and how thta should be used when recovering lost state in the
%% Ledger.
%% Both of the first two options relate to compaction in the Journal. The
%% retain_strategydetermines if a skinny record of the object should be
%% retained following compaction, and how that should be used when recovering
%% lost state in the Ledger.
%%
%% This is relevant to when Riak uses Leveled in that KeyChanges are presented
%% by the vnode to the backend as deltas. This means that if those key
%% changes do not remain recorded in the journal once the value has been
%% compacted - rebuilding the ledger from the Journal would lead to incorrect
%% index entries being present.
%%
%% Currently compacted records no longer in use are not removed but moved to
%% a journal_waste folder, and the waste_retention_period determines how long
%% this history should be kept for (for example to allow for it to be backed
%% up before deletion)
%% up before deletion).
%%
%% Compression method and point allow Leveled to be switched from using bif
%% based compression (zlib) to suing nif based compression (lz4). The
%% compression point can be changed between on_receipt (all values are
%% compressed as they are received), to on_compact where values are originally
%% stored uncompressed (speeding PUT times), and are only compressed when
%% they are first subject to compaction
%%
%% TODO:
%% The reload_strategy is exposed as currently no firm decision has been made