LiteTree: SQLite with Branches
Imagine being able to have many connections to the same database, each one reading a separate branch or commit at the same time. Or even writing to separate branches.
This is possible with LiteTree. It is a modification of the SQLite engine to support branching, like git!
Database branching is a very useful tool for blockchain implementations and LiteTree will be at the core of Aergo.
This is how it works:
Each database transaction is saved as a commit, and each commit has an incremental number. Let's consider an empty db in which we run this first SQL command:
CREATE TABLE t1 (name)
Now it will have the first commit (number 1) in the automatically created
When we execute new transactions it will add new commits to the current branch:
INSERT INTO t1 VALUES ('first') INSERT INTO t1 VALUES ('second')
Now we have 3 commits:
To include many SQL commands in a single commit we must enclose them in
We create new branches informing the source branch and commit number:
PRAGMA new_branch=test at master.2
After this command is executed the new branch is created but without any new data added to it. The database connection also moves to this new branch, having it as the current branch.
We can check the current branch with the command:
In this case it will return:
If we execute a SQL command on this db connection the commit will be saved in the connection's current branch:
INSERT INTO t1 VALUES ('from test branch')
Now the graph state will be:
We can also read the database at this new branch:
SELECT * FROM t1
It will return these values:
from test branch
We can move to the master branch:
And executing the same SELECT command (but now in the master branch) it will return:
Different content for the same table on separate branches.
Commits in separate branches have the same numbering based on the distance from the first commit:
We can read the database in a previous point-in-time by moving to that commit, like this:
At this point the table
t1 has a single row and if we do a SELECT it will return just
We cannot write to the database when we are in a defined commit, writing is only possible at the head of each branch. If you want to make modifications to some previous commit you must create a new branch that starts at that commit.
It is also possible to truncate a branch at a specific commit, rename a branch, delete it and retrieve branch info.
- Selecting the active branch:
- Selecting a specific commit in a branch:
- Retrieving the current/active branch:
- Listing the existing branches:
- Creating a new branch:
PRAGMA new_branch=<name> at <source>.<commit>
- Deleting a branch:
- Renaming a branch:
PRAGMA rename_branch <old_name> <new_name>
- Truncating a branch at a specific commit:
- Displaying the tree structure:
- Retrieving the branch info:
- Showing the commit and SQL log/history for a branch:
Not yet available
Some of these commands are being developed:
- Modifying a commit:
PRAGMA branch_log [--set|--add|--del] <name> <sql commands>
- Showing the diff between 2 branches or commits:
PRAGMA branch_diff <from_branch>[.<commit>] <to_branch>[.<commit>]
- Save metadata to each branch and/or commit
- Merging 2 branches
And maybe these extended features could be supported:
- Access control by branch
Check the roadmap on our wiki. Feature requests and suggestions are welcome.
We can use LiteTree with big databases (many gigabytes). There is no data copying when a new branch is created. When a new transaction is commited only the modified database pages are copied.
LiteTree is implemented storing the SQLite db pages on LMDB.
The data is not compressed, and each db page is stored on just one disk sector (4096 bytes by default). This is achieved by reserving some bytes at each SQLite db page so it can fit into one LMDB overflow page, that can hold 4080 (4096 - 16) bytes.
LiteTree is way faster than normal SQLite (journal mode) with comparable performance to WAL mode.
Here are the some results:
writing: -------- normal = 22.8921730518 seconds wal = 10.7780168056 seconds mmap = 10.4009709358 seconds litetree = 10.8633410931 seconds reading: -------- normal = 0.817955970764 seconds wal = 0.660045146942 seconds mmap = 0.592491865158 seconds litetree = 0.619393110275 seconds
writing: -------- normal = 1.9102909565 seconds wal = 1.30300784111 seconds mmap = 1.21677088737 seconds litetree = 0.988132953644 seconds reading: -------- normal = 0.999235868454 seconds wal = 0.776713132858 seconds mmap = 0.653935909271 seconds litetree = 0.714652061462 seconds
writing: -------- normal = 68.0931215734 seconds litetree = 39.239919979 seconds reading: -------- normal = 0.012673914421 seconds litetree = 0.00631055510799 seconds
You can make your own benchmark (after installing LiteTree) with this command:
Number of branches: 1024 branches (can be increased)
Number of commits per branch: 2^64 = 18,446,744,073,709,551,615 commits
Concurrent db connections to the same db: XXX readers
A database file created in one architecture cannot be used in another. This is a limitation of LMDB. We need to dump the database using
mdb_dump and load it using
The db file cannot be opened by unmodified SQLite libraries.
Savepoints are not yet supported.
How to use
LiteTree can be used in many programming languages via existing SQLite wrappers.
Update your app to open the database file using an URI containing the
branchesparameter, like this:
Make your app use this new library instead of the pre-installed SQLite library:
This can be achieved in 4 ways:
This can be used with all programming languages and wrappers.
Patching your wrapper or app to search for the library in the new path:
patchelf --set-rpath /usr/local/lib/litetree lib_or_app
rpathat the link time:
LIBPATH = /usr/local/lib/litetree gcc myapp.c -Wl,-rpath,$(LIBPATH) -L$(LIBPATH) -lsqlite3
You can use this if your app is linking directly to the LiteTree library.
Replacing the pre-installed SQLite library on your system
This can also be used with many programming languages. But use it with care because the native library may have been compiled with different directives.
On Mac OSX
This can be achieved in these ways:
Patching your wrapper or app to search for the library in the new path:
install_name_tool -change /old/path/to/libsqlite3.dylib /usr/local/lib/litetree/libsqlite3.dylib lib_or_app
You can check the old path with this command:
otool -L lib_or_app
This method can be used with all programming languages and wrappers as long as they are not protected by the OS.
It it is protected then you will need to install a new copy of the wrapper, modify it and use it instead of the protected one.
This can be used if the wrapper was linked to just the library name and does not contain any path.
If it does not work we can patch the wrapper to not contain any path:
install_name_tool -change /old/path/to/libsqlite3.dylib libsqlite3.dylib lib_or_app
But if you are able to modify the wrapper with
install_name_toolthen the first method above may be better.
Linking to the LiteTree library:
gcc myapp.c -L/usr/local/lib/litetree -lsqlite3
Copy the modified SQLite library to the system folder.
On 64 bit Windows:
C:\Windows\System32 (if 64 bit DLL)
C:\Windows\SysWOW64 (if 32 bit DLL)
On 32 bit Windows:
Compiling and installing
On Linux and Mac OSX
Install LMDB if not already installed:
git clone https://github.com/lmdb/lmdb cd lmdb/libraries/liblmdb make sudo make install
Then install LiteTree:
git clone https://github.com/aergoio/litetree cd litetree make sudo make install
You can use these pre-compiled binaries: (can be outdated)
Or follow these steps:
Compile LiteTree using MinGW or Visual Studio
Copy the libraries to the Windows System folder
Running the Tests
The tests are written in Python using the pysqlite wrapper.
On MacOSX we cannot use a modified SQLite library with the pre-installed system python due to the System Integrity Protection so we need to install another copy of pysqlite and link it to the LiteTree library:
git clone https://github.com/ghaering/pysqlite cd pysqlite echo "include_dirs=/usr/local/include" >> setup.cfg echo "library_dirs=/usr/local/lib/litetree" >> setup.cfg python setup.py build sudo python setup.py install
To run the tests:
Developed by Bernardo Ramos at