LETS - LevelDB-based Erlang Term Storage

Authors: Joseph Wayne Norton ([email protected]).

LETS is an alternative Erlang Term Storage using LevelDB as the storage implementation. LETS tries to address some bad properties of ETS and DETS. ETS is limited by physical memory. DETS is limited by a 2 GB file size limitation and does not implement ordered sets. LETS has neither of these limitations. Data can also be automatically compressed using the Snappy compression library. In addition, the name of a LETS table can be any Erlang term.

LETS is not intended to be an exact clone of ETS. The currently supported ETS APIs are:

all/0
delete/1
delete/2
delete_all_objects/1 only ets implementation
first/1
foldl/3
foldr/3
info/1 only a subset of items
info/2 only a subset of items
insert/2
insert_new/2 only ets implementation
last/1
lookup/2
lookup_element/3
match/1
match/2
match/3
match_delete/2
match_object/1
match_object/2
match_object/3
member/2
new/2
next/2
prev/2
select/1
select/2
select/3
select_count/2
select_delete/2
select_reverse/1
select_reverse/2
select_reverse/3
tab2list/1

For testing and comparison purposes, LETS supports five backend implementations:

drv CPP Driver with LevelDB backend (default)
nif CPP NIF with LevelDB backend
hyper drv CPP Driver with HyperLevelDB backend
hyper nif CPP NIF with HyperLevelDB backend
rocks drv CPP Driver with RocksDB backend
rocks nif CPP NIF with RocksDB backend
ets Erlang ETS backend

If desired, all of the five backends can be called directly using the table identifier returned by new/2, tid/1, and/or tid/2. The tid/1 and tid/2 approach must be used for named tables. The five backends implement the gen_ets_ns behaviour to provide batch insertion, batch iteration by key, batch iteration by object, and other basic table operations. See the following modules for the corresponding backend:

drv - src/lets_impl_drv.erl
nif - src/lets_impl_nif.erl
hyper drv - src/hets_impl_drv.erl
hyper nif - src/hets_impl_nif.erl
rocks drv - src/rets_impl_drv.erl
rocks nif - src/rets_impl_nif.erl
ets - deps/gen_ets/src/gen_ets_impl_ets.erl

The Driver backends are recommended over the NIF backends for two reasons:

The NIF backends when deleting the table rely on garbage collection of the NIF resource to delete the corresponding CPP database object. The calling application must manage this carefully to ensure that a call to re-open an existing database is not performed until the CPP database object is deleted. The Driver backends do not have this limitation.
The NIF backends are not built as "dirty" NIFs and can easily block the emulator's schedulers. The Driver backends support the async option for such purpose. It is recommended to use the Driver backends until the "dirty" NIF functionality is a non-experimental Erlang/OTP feature and the LETS NIF backends are built as "dirty" NIFs.

Development and testing of LETS is done solely on Mac OS X. Feedback and/or bug reports on other operating systems is welcome.

This repository is experimental in nature - use at your own risk and please contribute if you find LETS useful.

Quick Start Recipe

To download and build the lets application in one shot, please follow this recipe:

$ mkdir working-directory-name
$ cd working-directory-name
$ git clone https://github.com/norton/lets.git lets
$ cd lets
$ make deps clean compile

OR if QuickCheck is available then follow this recipe:

$ mkdir working-directory-name
$ cd working-directory-name
$ git clone https://github.com/norton/lets.git lets
$ cd lets
$ make deps clean compile-for-eqc
$ (cd .qc; erl -smp +A 5 -pz -pz ../deps/{sext,gen_ets,qc}/ebin)

1> qc_statem_lets:qc_run(500).
.......
OK, passed 500 tests

100.0% {1,attempts}

3.46% {{undefined,[]},{new,2},ok}
1.21% {{ets,[]},{select_delete,2},ok}
1.19% {{ets,[]},{tid,1},ok}
1.11% {{ets,[]},{match_object,2},ok}
1.11% {{ets,[]},{insert,2},ok}
1.11% {{ets,[]},{all,1},ok}
1.11% {{ets,[]},{select_reverse,2},ok}
1.11% {{ets,[]},{match_delete,2},ok}
1.08% {{ets,[]},{member,2},ok}
1.08% {{ets,[]},{insert_new,2},ok}
1.03% {{ets,[]},{foldl,3},ok}
1.02% {{ets,[]},{select,2},ok}
1.01% {{ets,[]},{foldr,3},ok}
1.01% {{ets,[]},{delete,2},ok}
1.01% {{ets,[]},{select31,3},ok}
1.00% {{ets,[]},{match_object31,3},ok}
0.98% {{ets,[]},{tid,2},ok}
0.97% {{ets,[]},{select_reverse31,3},ok}
0.97% {{ets,[]},{select_count,2},ok}
0.97% {{ets,[]},{delete,1},ok}
0.95% {{ets,[]},{delete_all_objects,1},ok}
0.94% {{ets,[]},{last,1},ok}
0.93% {{ets,[]},{lookup_element,3},{error,badarg}}
0.93% {{ets,[]},{first,1},ok}
0.92% {{ets,[]},{tab2list,1},ok}
0.90% {{ets,[]},{match,2},ok}
0.90% {{ets,[]},{lookup,2},ok}
0.90% {{ets,[]},{match31,3},ok}
0.89% {{ets,[]},{new,3},ok}
0.67% {{drv,[hyper]},{tid,1},ok}
0.66% {{drv,[hyper]},{select,2},ok}
0.66% {{drv,[hyper]},{all,1},ok}
0.65% {{drv,[hyper]},{match_object31,3},ok}
0.64% {{nif,[]},{match_object,2},ok}
0.64% {{drv,[hyper]},{select_reverse31,3},ok}
0.64% {{nif,[]},{select_reverse31,3},ok}
0.64% {{drv,[hyper]},{tid,2},ok}
0.63% {{nif,[]},{tab2list,1},ok}
0.62% {{nif,[]},{select31,3},ok}
0.62% {{drv,[hyper]},{foldr,3},ok}
0.61% {{drv,[hyper]},{next,2},ok}
0.61% {{nif,[]},{select_delete,2},ok}
0.61% {{drv,[hyper]},{first,1},ok}
0.60% {{nif,[]},{match_object31,3},ok}
0.60% {{drv,[hyper]},{match_object,2},ok}
0.60% {{drv,[hyper]},{match_delete,2},ok}
0.60% {{drv,[hyper]},{delete,2},ok}
0.59% {{drv,[hyper]},{foldl,3},ok}
0.58% {{nif,[]},{select,2},ok}
0.58% {{drv,[hyper]},{tab2list,1},ok}
0.58% {{drv,[hyper]},{select_count,2},ok}
0.57% {{drv,[hyper]},{member,2},ok}
0.56% {{drv,[hyper]},{match31,3},ok}
0.56% {{drv,[hyper]},{insert,2},ok}
0.56% {{nif,[]},{prev,2},ok}
0.56% {{nif,[]},{next,2},ok}
0.55% {{nif,[]},{select_reverse,2},ok}
0.55% {{nif,[]},{lookup,2},ok}
0.55% {{drv,[hyper]},{select_delete,2},ok}
0.54% {{nif,[]},{all,1},ok}
0.54% {{ets,[]},{next,2},{error,badarg}}
0.53% {{nif,[]},{match31,3},ok}
0.53% {{nif,[]},{delete,1},ok}
0.53% {{nif,[]},{new,3},ok}
0.51% {{nif,[]},{foldr,3},ok}
0.51% {{drv,[hyper]},{lookup,2},ok}
0.51% {{nif,[]},{last,1},ok}
0.51% {{ets,[]},{next,2},ok}
0.51% {{drv,[hyper]},{select_reverse,2},ok}
0.51% {{drv,[hyper]},{prev,2},ok}
0.50% {{drv,[hyper]},{last,1},ok}
0.48% {{nif,[]},{member,2},ok}
0.48% {{ets,[]},{prev,2},ok}
0.48% {{drv,[hyper]},{select31,3},ok}
0.48% {{nif,[]},{match_delete,2},ok}
0.48% {{nif,[]},{delete,2},ok}
0.47% {{drv,[hyper]},{match,2},ok}
0.47% {{drv,[hyper]},{delete,1},ok}
0.46% {{drv,[]},{delete,2},ok}
0.45% {{nif,[]},{foldl,3},ok}
0.44% {{nif,[hyper]},{match_object31,3},ok}
0.44% {{nif,[]},{tid,2},ok}
0.44% {{nif,[]},{insert,2},ok}
0.43% {{nif,[rocks]},{member,2},ok}
0.43% {{drv,[hyper]},{new,3},ok}
0.43% {{drv,[hyper]},{lookup_element,3},{error,badarg}}
0.43% {{nif,[rocks]},{all,1},ok}
0.43% {{ets,[]},{prev,2},{error,badarg}}
0.42% {{nif,[hyper]},{match_object,2},ok}
0.42% {{drv,[]},{last,1},ok}
0.41% {{nif,[]},{tid,1},ok}
0.40% {{drv,[]},{tid,1},ok}
0.40% {{drv,[]},{select_reverse,2},ok}
0.39% {{nif,[hyper]},{tid,1},ok}
0.39% {{nif,[hyper]},{select31,3},ok}
0.39% {{drv,[]},{insert,2},ok}
0.38% {{nif,[rocks]},{select,2},ok}
0.38% {{nif,[rocks]},{insert,2},ok}
0.38% {{nif,[rocks]},{foldr,3},ok}
0.38% {{nif,[hyper]},{lookup,2},ok}
0.38% {{nif,[hyper]},{last,1},ok}
0.38% {{nif,[hyper]},{first,1},ok}
0.38% {{nif,[]},{match,2},ok}
0.38% {{nif,[]},{first,1},ok}
0.38% {{drv,[]},{match_object31,3},ok}
0.38% {{nif,[rocks]},{select31,3},ok}
0.38% {{nif,[hyper]},{insert,2},ok}
0.38% {{nif,[]},{select_count,2},ok}
0.38% {{drv,[]},{tid,2},ok}
0.37% {{nif,[rocks]},{select_reverse31,3},ok}
0.37% {{nif,[rocks]},{prev,2},ok}
0.37% {{nif,[rocks]},{match,2},ok}
0.37% {{drv,[rocks]},{select_delete,2},ok}
0.37% {{drv,[]},{first,1},ok}
0.36% {{drv,[]},{tab2list,1},ok}
0.35% {{nif,[rocks]},{tab2list,1},ok}
0.35% {{nif,[hyper]},{select_reverse31,3},ok}
0.35% {{nif,[hyper]},{next,2},ok}
0.35% {{drv,[rocks]},{tid,2},ok}
0.35% {{drv,[]},{delete,1},ok}
0.35% {{nif,[rocks]},{match_object,2},ok}
0.35% {{nif,[hyper]},{select,2},ok}
0.35% {{nif,[hyper]},{match_delete,2},ok}
0.35% {{nif,[hyper]},{delete,2},ok}
0.35% {{drv,[]},{select_reverse31,3},ok}
0.35% {{drv,[]},{foldr,3},ok}
0.34% {{nif,[rocks]},{select_delete,2},ok}
0.34% {{nif,[hyper]},{select_reverse,2},ok}
0.34% {{nif,[hyper]},{foldr,3},ok}
0.33% {{nif,[hyper]},{tab2list,1},ok}
0.33% {{nif,[]},{lookup_element,3},{error,badarg}}
0.33% {{drv,[rocks]},{next,2},ok}
0.33% {{drv,[]},{match_object,2},ok}
0.33% {{nif,[rocks]},{select_count,2},ok}
0.33% {{nif,[rocks]},{match_object31,3},ok}
0.33% {{nif,[rocks]},{match_delete,2},ok}
0.33% {{nif,[hyper]},{prev,2},ok}
0.33% {{nif,[hyper]},{match31,3},ok}
0.33% {{drv,[rocks]},{prev,2},ok}
0.32% {{nif,[rocks]},{foldl,3},ok}
0.32% {{nif,[hyper]},{match,2},ok}
0.32% {{nif,[hyper]},{lookup_element,3},{error,badarg}}
0.32% {{drv,[rocks]},{last,1},ok}
0.32% {{drv,[]},{new,3},ok}
0.32% {{drv,[]},{match,2},ok}
0.31% {{nif,[rocks]},{tid,2},ok}
0.31% {{nif,[rocks]},{match31,3},ok}
0.31% {{nif,[rocks]},{delete,2},ok}
0.31% {{nif,[rocks]},{delete,1},ok}
0.31% {{drv,[rocks]},{tid,1},ok}
0.31% {{drv,[]},{lookup,2},ok}
0.31% {{drv,[]},{all,1},ok}
0.30% {{nif,[rocks]},{select_reverse,2},ok}
0.30% {{nif,[rocks]},{new,3},ok}
0.30% {{nif,[hyper]},{all,1},ok}
0.30% {{drv,[rocks]},{first,1},ok}
0.30% {{drv,[]},{prev,2},ok}
0.30% {{drv,[]},{next,2},ok}
0.30% {{drv,[]},{lookup_element,3},{error,badarg}}
0.30% {{nif,[hyper]},{tid,2},ok}
0.30% {{drv,[rocks]},{tab2list,1},ok}
0.30% {{drv,[rocks]},{select_reverse,2},ok}
0.30% {{drv,[]},{match_delete,2},ok}
0.29% {{nif,[rocks]},{next,2},ok}
0.29% {{nif,[hyper]},{select_count,2},ok}
0.29% {{drv,[rocks]},{delete,2},ok}
0.28% {{drv,[rocks]},{insert,2},ok}
0.28% {{drv,[]},{foldl,3},ok}
0.28% {{nif,[rocks]},{tid,1},ok}
0.28% {{nif,[hyper]},{select_delete,2},ok}
0.28% {{nif,[hyper]},{member,2},ok}
0.28% {{nif,[hyper]},{foldl,3},ok}
0.28% {{nif,[hyper]},{delete,1},ok}
0.28% {{drv,[rocks]},{delete,1},ok}
0.28% {{drv,[]},{select,2},ok}
0.27% {{drv,[rocks]},{new,3},ok}
0.27% {{drv,[rocks]},{lookup,2},ok}
0.27% {{drv,[]},{select_delete,2},ok}
0.27% {{drv,[]},{select_count,2},ok}
0.27% {{drv,[]},{match31,3},ok}
0.26% {{nif,[rocks]},{lookup_element,3},{error,badarg}}
0.26% {{nif,[hyper]},{new,3},ok}
0.26% {{drv,[rocks]},{select31,3},ok}
0.26% {{drv,[rocks]},{match_object,2},ok}
0.26% {{drv,[rocks]},{match_delete,2},ok}
0.26% {{drv,[]},{member,2},ok}
0.25% {{nif,[rocks]},{lookup,2},ok}
0.25% {{drv,[rocks]},{match,2},ok}
0.25% {{nif,[rocks]},{last,1},ok}
0.25% {{nif,[rocks]},{first,1},ok}
0.25% {{drv,[rocks]},{match31,3},ok}
0.25% {{drv,[rocks]},{foldr,3},ok}
0.24% {{drv,[rocks]},{select_count,2},ok}
0.23% {{drv,[rocks]},{member,2},ok}
0.23% {{drv,[rocks]},{all,1},ok}
0.22% {{drv,[rocks]},{select,2},ok}
0.22% {{drv,[]},{select31,3},ok}
0.21% {{drv,[rocks]},{match_object31,3},ok}
0.21% {{drv,[rocks]},{foldl,3},ok}
0.20% {{drv,[rocks]},{lookup_element,3},{error,badarg}}
0.17% {{drv,[rocks]},{select_reverse31,3},ok}
0.13% {{ets,[]},{lookup_element,3},ok}
0.11% {{nif,[]},{lookup_element,3},ok}
0.08% {{drv,[hyper]},{lookup_element,3},ok}
0.07% {{nif,[rocks]},{lookup_element,3},ok}
0.04% {{drv,[]},{lookup_element,3},ok}
0.03% {{nif,[hyper]},{lookup_element,3},ok}
0.03% {{drv,[rocks]},{lookup_element,3},ok}
true
.......

Tip	For testing LevelDB directly using the C bindings, try`qc_statemc_lets:qc_run(500)`.

OR if PropEr is available then follow this recipe:

$ mkdir working-directory-name
$ cd working-directory-name
$ git clone https://github.com/norton/lets.git lets
$ cd lets
$ make deps clean compile-for-proper
$ (cd .qc; erl -smp +A 5 -pz -pz ../deps/{sext,gen_ets,qc}/ebin)

1> qc_statem_lets:qc_run(500).
.......
OK: Passed 500 test(s).

9% {{undefined,[]},{new,2},ok}
1% {{ets,[]},{foldr,3},ok}
1% {{ets,[]},{tid,2},ok}
1% {{ets,[]},{delete,1},ok}
1% {{ets,[]},{tid,1},ok}
1% {{ets,[]},{delete_all_objects,1},ok}
1% {{ets,[]},{new,3},ok}
1% {{ets,[]},{select,2},ok}
1% {{ets,[]},{all,1},ok}
1% {{ets,[]},{last,1},ok}
1% {{ets,[]},{select_delete,2},ok}
1% {{ets,[]},{select_reverse31,3},ok}
1% {{ets,[]},{match_delete,2},ok}
1% {{ets,[]},{select31,3},ok}
1% {{ets,[]},{insert_new,2},ok}
1% {{ets,[]},{match_object,2},ok}
0% {{ets,[]},{delete,2},ok}
0% {{ets,[]},{tab2list,1},ok}
0% {{ets,[]},{insert,2},ok}
0% {{ets,[]},{match_object31,3},ok}
0% {{ets,[]},{foldl,3},ok}
0% {{ets,[]},{lookup,2},ok}
0% {{ets,[]},{lookup_element,3},{error,badarg}}
0% {{ets,[]},{first,1},ok}
0% {{ets,[]},{member,2},ok}
0% {{ets,[]},{select_count,2},ok}
0% {{ets,[]},{match,2},ok}
0% {{ets,[]},{select_reverse,2},ok}
0% {{ets,[]},{match31,3},ok}
0% {{ets,[]},{prev,2},ok}
0% {{nif,[]},{select,2},ok}
0% {{ets,[]},{next,2},{error,badarg}}
0% {{nif,[]},{tid,1},ok}
0% {{drv,[]},{match,2},ok}
0% {{drv,[]},{select_delete,2},ok}
0% {{nif,[]},{delete,2},ok}
0% {{nif,[]},{first,1},ok}
0% {{nif,[]},{insert,2},ok}
0% {{nif,[]},{select31,3},ok}
0% {{drv,[]},{delete,1},ok}
0% {{nif,[]},{match_object,2},ok}
0% {{drv,[hyper]},{foldr,3},ok}
0% {{drv,[rocks]},{prev,2},ok}
0% {{ets,[]},{next,2},ok}
0% {{ets,[]},{prev,2},{error,badarg}}
0% {{nif,[]},{delete,1},ok}
0% {{nif,[]},{match_delete,2},ok}
0% {{nif,[rocks]},{tid,1},ok}
0% {{drv,[hyper]},{match31,3},ok}
0% {{nif,[]},{match,2},ok}
0% {{nif,[]},{new,3},ok}
0% {{nif,[]},{select_reverse31,3},ok}
0% {{drv,[]},{match31,3},ok}
0% {{drv,[]},{tab2list,1},ok}
0% {{nif,[]},{foldr,3},ok}
0% {{nif,[rocks]},{last,1},ok}
0% {{nif,[rocks]},{lookup_element,3},{error,badarg}}
0% {{nif,[rocks]},{match,2},ok}
0% {{drv,[]},{new,3},ok}
0% {{drv,[hyper]},{select31,3},ok}
0% {{drv,[hyper]},{select_reverse,2},ok}
0% {{drv,[hyper]},{select_reverse31,3},ok}
0% {{nif,[]},{next,2},ok}
0% {{nif,[rocks]},{foldl,3},ok}
0% {{nif,[rocks]},{select_delete,2},ok}
0% {{nif,[rocks]},{tab2list,1},ok}
0% {{drv,[]},{all,1},ok}
0% {{drv,[]},{delete,2},ok}
0% {{drv,[]},{first,1},ok}
0% {{drv,[]},{foldr,3},ok}
0% {{drv,[]},{match_object31,3},ok}
0% {{drv,[]},{next,2},ok}
0% {{drv,[hyper]},{match_object31,3},ok}
0% {{drv,[hyper]},{tab2list,1},ok}
0% {{nif,[]},{select_delete,2},ok}
0% {{nif,[rocks]},{prev,2},ok}
0% {{drv,[hyper]},{insert,2},ok}
0% {{drv,[hyper]},{select,2},ok}
0% {{drv,[rocks]},{tid,1},ok}
0% {{nif,[]},{last,1},ok}
0% {{nif,[]},{lookup_element,3},{error,badarg}}
0% {{nif,[]},{match_object31,3},ok}
0% {{nif,[]},{member,2},ok}
0% {{drv,[]},{insert,2},ok}
0% {{drv,[hyper]},{tid,2},ok}
0% {{drv,[rocks]},{match31,3},ok}
0% {{nif,[]},{lookup,2},ok}
0% {{nif,[]},{match31,3},ok}
0% {{nif,[]},{select_count,2},ok}
0% {{drv,[]},{last,1},ok}
0% {{drv,[]},{lookup,2},ok}
0% {{drv,[]},{select_count,2},ok}
0% {{drv,[hyper]},{lookup_element,3},{error,badarg}}
0% {{drv,[hyper]},{match,2},ok}
0% {{drv,[hyper]},{select_delete,2},ok}
0% {{nif,[]},{prev,2},ok}
0% {{nif,[]},{tab2list,1},ok}
0% {{nif,[rocks]},{next,2},ok}
0% {{drv,[]},{foldl,3},ok}
0% {{drv,[]},{match_object,2},ok}
0% {{drv,[]},{member,2},ok}
0% {{drv,[]},{select,2},ok}
0% {{drv,[]},{select31,3},ok}
0% {{drv,[]},{tid,2},ok}
0% {{drv,[hyper]},{foldl,3},ok}
0% {{drv,[rocks]},{all,1},ok}
0% {{drv,[rocks]},{match_object,2},ok}
0% {{nif,[rocks]},{foldr,3},ok}
0% {{nif,[rocks]},{lookup,2},ok}
0% {{nif,[rocks]},{member,2},ok}
0% {{drv,[hyper]},{all,1},ok}
0% {{drv,[rocks]},{tab2list,1},ok}
0% {{nif,[]},{all,1},ok}
0% {{nif,[]},{select_reverse,2},ok}
0% {{nif,[hyper]},{tab2list,1},ok}
0% {{nif,[rocks]},{first,1},ok}
0% {{nif,[rocks]},{insert,2},ok}
0% {{nif,[rocks]},{select31,3},ok}
0% {{nif,[rocks]},{select_reverse31,3},ok}
0% {{drv,[]},{lookup_element,3},{error,badarg}}
0% {{drv,[]},{select_reverse,2},ok}
0% {{drv,[hyper]},{first,1},ok}
0% {{drv,[hyper]},{member,2},ok}
0% {{drv,[rocks]},{delete,1},ok}
0% {{drv,[rocks]},{last,1},ok}
0% {{drv,[rocks]},{lookup,2},ok}
0% {{drv,[rocks]},{match,2},ok}
0% {{drv,[rocks]},{new,3},ok}
0% {{drv,[rocks]},{select_reverse,2},ok}
0% {{nif,[]},{foldl,3},ok}
0% {{nif,[hyper]},{delete,2},ok}
0% {{nif,[hyper]},{last,1},ok}
0% {{nif,[hyper]},{select_count,2},ok}
0% {{nif,[rocks]},{delete,1},ok}
0% {{nif,[rocks]},{match_delete,2},ok}
0% {{nif,[rocks]},{match_object31,3},ok}
0% {{nif,[rocks]},{select_count,2},ok}
0% {{drv,[]},{match_delete,2},ok}
0% {{drv,[]},{prev,2},ok}
0% {{drv,[hyper]},{delete,1},ok}
0% {{drv,[hyper]},{next,2},ok}
0% {{drv,[hyper]},{prev,2},ok}
0% {{drv,[hyper]},{tid,1},ok}
0% {{drv,[rocks]},{foldl,3},ok}
0% {{drv,[rocks]},{match_delete,2},ok}
0% {{nif,[]},{tid,2},ok}
0% {{nif,[hyper]},{foldr,3},ok}
0% {{nif,[hyper]},{lookup,2},ok}
0% {{nif,[rocks]},{delete,2},ok}
0% {{nif,[rocks]},{select,2},ok}
0% {{nif,[rocks]},{tid,2},ok}
0% {{drv,[hyper]},{last,1},ok}
0% {{drv,[hyper]},{lookup,2},ok}
0% {{drv,[hyper]},{match_delete,2},ok}
0% {{drv,[hyper]},{select_count,2},ok}
0% {{drv,[rocks]},{match_object31,3},ok}
0% {{ets,[]},{lookup_element,3},ok}
0% {{nif,[hyper]},{match31,3},ok}
0% {{nif,[hyper]},{prev,2},ok}
0% {{nif,[hyper]},{select,2},ok}
0% {{nif,[rocks]},{new,3},ok}
0% {{drv,[]},{select_reverse31,3},ok}
0% {{drv,[hyper]},{match_object,2},ok}
0% {{drv,[hyper]},{new,3},ok}
0% {{drv,[rocks]},{first,1},ok}
0% {{drv,[rocks]},{foldr,3},ok}
0% {{drv,[rocks]},{insert,2},ok}
0% {{nif,[hyper]},{first,1},ok}
0% {{nif,[hyper]},{insert,2},ok}
0% {{nif,[hyper]},{select_reverse31,3},ok}
0% {{nif,[rocks]},{all,1},ok}
0% {{nif,[rocks]},{match31,3},ok}
0% {{drv,[]},{tid,1},ok}
0% {{drv,[rocks]},{select_delete,2},ok}
0% {{nif,[hyper]},{match_object31,3},ok}
0% {{nif,[hyper]},{select_delete,2},ok}
0% {{nif,[hyper]},{tid,1},ok}
0% {{nif,[rocks]},{select_reverse,2},ok}
0% {{drv,[hyper]},{delete,2},ok}
0% {{nif,[hyper]},{all,1},ok}
0% {{nif,[hyper]},{match,2},ok}
0% {{nif,[hyper]},{match_delete,2},ok}
0% {{nif,[hyper]},{member,2},ok}
0% {{drv,[rocks]},{delete,2},ok}
0% {{drv,[rocks]},{select,2},ok}
0% {{drv,[rocks]},{select31,3},ok}
0% {{nif,[hyper]},{delete,1},ok}
0% {{nif,[hyper]},{lookup_element,3},{error,badarg}}
0% {{nif,[hyper]},{next,2},ok}
0% {{nif,[hyper]},{select_reverse,2},ok}
0% {{nif,[hyper]},{tid,2},ok}
0% {{nif,[rocks]},{match_object,2},ok}
0% {{drv,[rocks]},{member,2},ok}
0% {{drv,[rocks]},{select_reverse31,3},ok}
0% {{drv,[rocks]},{tid,2},ok}
0% {{nif,[hyper]},{foldl,3},ok}
0% {{nif,[hyper]},{new,3},ok}
0% {{drv,[rocks]},{next,2},ok}
0% {{drv,[rocks]},{select_count,2},ok}
0% {{nif,[]},{lookup_element,3},ok}
0% {{nif,[hyper]},{match_object,2},ok}
0% {{drv,[rocks]},{lookup_element,3},{error,badarg}}
0% {{nif,[hyper]},{select31,3},ok}
0% {{drv,[rocks]},{lookup_element,3},ok}
0% {{nif,[hyper]},{lookup_element,3},ok}
0% {{drv,[hyper]},{lookup_element,3},ok}
0% {{nif,[rocks]},{lookup_element,3},ok}
true
.......

Documentation

Where should I start?

This README is the only bit of documentation.

The QC (a.k.a. QuickCheck) tests underneath the "tests/qc" directory should be helpful for understanding the specification and behavior of ETS and LETS. These QC tests also illustrate several strategies for testing Erlang Driver-based and NIF-based implementations.

What is ETS and DETS?

ETS and DETS are Erlang/OTP's standard library modules for Erlang term storage. ETS is a memory-based implementation. DETS is a disk-based implementation.

See http://www.erlang.org/doc/man/ets.html and http://www.erlang.org/doc/man/dets.html for further details.

What is LevelDB?

LevelDB is a fast key-value storage library written at Google that provides an ordered mapping from string keys to string values.

See https://github.com/google/leveldb for further details.

What is HyperLevelDB?

HyperLevelDB is the data storage engine that powers HyperDex. HyperLevelDB was forked from Google's LevelDB and adapted to more closely meet the needs of HyperDex.

See https://github.com/rescrv/HyperLevelDB for further details.

What is RocksDB?

RocksDB is a persistent Key-Value Store for Flash and RAM Storage. RocksDB is built on earlier work from Google's LevelDB.

See https://github.com/facebook/rocksdb for further details.

What is Snappy?

Snappy is a fast compression/decompression library written at Google.

See https://github.com/google/snappy for further details.

Tools

For further information and help for related tools, please refer to the following links:

Erlang - http://www.erlang.org/
- R16B or newer, 17.5 has been tested most recently
Git - http://git-scm.com/
- Git 1.5.4 or newer, Git 2.3.5 has been tested most recently
GitHub - https://github.com

Roadmap

Documentation
- Explain how to run QuickCheck tests using a new rebar plugin.
- Explain how to build and to run lets with valgrind enabled OTP/Erlang virtual machine
Backends (TBD)
- Implement the NIF backends as "dirty" NIFs.
New APIs (TBD)
- insert_new/2 (http://code.google.com/p/leveldb/issues/detail?id=42)
- delete_all_objects/1 (http://code.google.com/p/leveldb/issues/detail?id=43)
- Add custom (i.e. not supported by native ETS) APIs for providing access to LevelDB's iterators for drv and nif backend implementations.
Existing APIs (TBD)
- delete/1 (http://code.google.com/p/leveldb/issues/detail?id=48)
- new/2 - (http://code.google.com/p/leveldb/issues/detail?id=49)
- new/2 - investigate if LevelDB's snapshot feature is useful (or not) for LETS
- info/2 - investigate if LevelDB's implementation can (easily) support size and memory info items
Testing - Black Box
- Functional
  - Update test model to include LevelDB's database, read, and write options. These options have not been tested.
  - Update test model to include LevelDB's destroy and repair operations. These operations have not been tested.
- Performance (TBD)
- Stability (TBD)
Testing - White (or more like "Grey") Box
- Goals
  - Test normal, abnormal, and corner test cases without having to actually use "big data" or invoke lots of operations. Invoke operations using small inputs but with varying sizes, ranges, and patterns.
  - Learn about what special parameters exist, their default values and ranges, and the difficulty to control these parameters on a request-by-request basis (at best case).
- Functional (TBD)
  - Enable/disable background compaction
  - Invoke/suspend manual compaction
  - Force new memtable creation
  - Force new level creation
  - Database Recovery (i.e. closing/reopening the db)
  - Large keys (e.g. 1KB)
  - Adjacent keys that share a long prefix (e.g ~1KB); useful since file format has prefix compression
  - Snapshots that are live across compactions and are read from after compaction
  - Iterators that are live across compactions and are read from after compaction
  - File system writes return errors (e.g., disk-full)