%% -*- Doc -*- %% vim: set syntax=asciidoc: @author Joseph Wayne Norton @copyright 2011 by Joseph Wayne Norton @title LETS - LevelDB-based Erlang Term Storage @doc 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. For testing and comparison purposes, LETS supports three implementations: - +drv+ C\+\+ Driver with LevelDB backend _(default)_ - +nif+ C\+\+ NIF with LevelDB backend - +ets+ Erlang ETS backend LETS is not intended to be an exact clone of ETS. The currently supported APIs are: - +new/2+ - +destroy/2+ _only driver and nif implementations_ - +repair/2+ _only driver and nif implementations_ - +insert/2+ - +insert_new/2+ _only the ets implementation_ - +delete/1+ - +delete/2+ - +delete_all_objects/1+ _only the ets implementation_ - +lookup/2+ - +first/1+ - +next/2+ - +info/2+ _only a subset of items_ - +tab2list/1+ _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 git://github.com/norton/snappy.git snappy $ git clone git://github.com/norton/leveldb.git leveldb $ git clone git://github.com/norton/lets.git lets $ cd lets $ ./rebar get-deps $ ./rebar clean $ ./rebar compile ------ For an alternative recipe with other "features" albeit more complex, please read further. == Documentation === Where should I start? This README is the only bit of documentation right now. The QC (a.k.a. QuickCheck, Proper, etc.) 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 http://code.google.com/p/leveldb/ for further details. == To download 1. Configure your e-mail and name for Git + ------ $ git config \--global user.email "you@example.com" $ git config \--global user.name "Your Name" ------ 2. Install Repo + ------ $ mkdir -p ~/bin $ wget -O - https://github.com/android/tools_repo/raw/master/repo > ~/bin/repo $ perl -i.bak -pe 's!git://android.git.kernel.org/tools/repo.git!git://github.com/android/tools_repo.git!;' ~/bin/repo $ chmod a+x ~/bin/repo ------ + CAUTION: Since access to kernel.org has been shutdown due to hackers, fetch and replace repo tool with android\'s GitHub repository mirror. 3. Create working directory + ------ $ mkdir working-directory-name $ cd working-directory-name $ repo init -u git://github.com/norton/manifests.git -m lets-default.xml ------ + NOTE: Your "Git" identity is needed during the init step. Please enter the name and email of your GitHub account if you have one. Team members having read-write access are recommended to use "repo init -u git@github.com:norton/manifests.git -m lets-default-rw.xml". + TIP: If you want to checkout the latest development version, please append " -b dev" to the repo init command. 4. Download Git repositories + ------ $ cd working-directory-name $ repo sync ------ For futher information and help for related tools, please refer to the following links: - Erlang - http://www.erlang.org/ * *R14B03 or newer, R14B04 has been tested most recently* - Git - http://git-scm.com/ * *Git 1.5.4 or newer, Git 1.7.7 has been tested recently* * _required for Repo and GitHub_ - GitHub - https://github.com - Python - http://www.python.org * *Python 2.4 or newer, Python 2.7.1 has been tested most recently (CAUTION: Python 3.x might be too new)* * _required for Repo_ - Rebar - https://github.com/basho/rebar/wiki - Repo - http://source.android.com/source/git-repo.html == To build - basic recipe 1. Get and install an erlang system http://www.erlang.org 2. Build + ------ $ cd working-directory-name/src $ make compile ------ == To build - optional features A. Dialyzer Testing _basic recipe_ 1. Build Dialyzer\'s PLT _(required once)_ + ------ $ cd working-directory-name/src $ make build-plt ------ + TIP: Check Makefile and dialyzer\'s documentation for further information. 2. Dialyze with specs + ------ $ cd working-directory-name/src $ make dialyze ------ + CAUTION: If you manually run dialyzer with the "-r" option, execute "make clean compile" first to avoid finding duplicate beam files underneath rebar\'s .eunit directory. Check Makefile for further information. 3. Dialyze without specs + ------ $ cd working-directory-name/src $ make dialyze-nospec ------ == To test - QuickCheck 1. Make sure QuickCheck is in your Erlang code path. One simple way to accomplish this is by adding the code path to your +~/.erlang+ resource file. + ------ true = code:add_pathz(os:getenv("HOME")++"/.erlang.d/lib/quviq/eqc-X.Y.Z/ebin"). ------ 2. Compile for QuickCheck + ------ $ cd working-directory-name/src $ make clean $ make compile-eqc eqc-compile ------ 3. Run 5,000 QuickCheck tests + ------ $ cd working-directory-name/src/lib/lets/.eunit $ erl -smp +A 5 -pz ../../sext/ebin -pz ../../qc/ebin 1> qc_statem_lets:run(5000). ....... ------ + TIP: For testing LevelDB directly using the C bindings, try +qc_statemc_lets:run(5000)+. == To test - Proper 1. Make sure Proper is in your Erlang code path. One simple way to accomplish this is by adding the code path to your +~/.erlang+ resource file. + ------ true = code:add_pathz(os:getenv("HOME")++"/.erlang.d/lib/proper/ebin"). ------ 2. Compile for Proper + ------ $ cd working-directory-name/src $ make clean $ make compile-proper proper-compile ------ 3. Run 5,000 Proper tests + ------ $ cd working-directory-name/src/lib/lets/.eunit $ erl -smp +A 5 -pz ../../sext/ebin -pz ../../qc/ebin 1> qc_statem_lets:run(5000). ....... ------ == Roadmap - Documentation * Explain how to run QuickCheck/Proper tests using a new rebar plugin. * Explain how to build and to run lets with valgrind enabled OTP/Erlang virtual machine - Bugs * LevelDB - Reappearing "ghost" key after 17 steps (http://code.google.com/p/leveldb/issues/detail?id=44) + NOTE: LET\'s QC tests are hard-coded not to close and then to reopen a LevelDB database until this bug has been fixed. - Performance * Update driver implementation to use Erlang\'s asynchronous driver thread pool for all LevelDB operations. - Testing * Functional ** Update test model to include LevelDB\'s database, read, and write options. These options have not undergone any explicit testing. * Performance (TBD) * Stability (TBD) - 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) - Existing APIs (TBD) * +new/2+ - automatically detect and prevent multiple callers of the same Erlang virtual machine from simultaneously opening the same LevelDB. Excerpt from the Google leveldb mailing list: + ------ Sanjay Ghemawat View profile More options Sep 30, 1:04 am On Thu, Sep 29, 2011 at 8:30 AM, Joseph Wayne Norton wrote: > Hans - > Thanks. Is is correct to assume that it is the caller's responsibility to > ensure this does not happen? leveldb guarantees that it will catch when two distinct processes try to open the db concurrently. However it doesn't guarantee what happens if the same process tries to do so and therefore it is the caller's responsibility to check for concurrent opens from the same process. This is ugly, but the unix file locking primitives are very annoying in this regard. I'll think about whether or not we should clean up the spec by doing extra checks inside the leveldb implementation. ------ * +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 * consider adding explicit read_options and write_options for LET\'s operations (rather than just +new/2+, +destroy/2+, and +repair/2+ operations). @end