Zenith

Zenith substitutes PostgreSQL storage layer and redistributes data across a cluster of nodes

Architecture overview

A Zenith installation consists of Compute nodes and Storage engine.

Compute nodes are stateless PostgreSQL nodes, backed by zenith storage.

Zenith storage engine consists of two major components:

• Pageserver. Scalable storage backend for compute nodes.
• WAL service. The service that receives WAL from compute node and ensures that it is stored durably.

Pageserver consists of:

• Repository - Zenith storage implementation.
• WAL receiver - service that receives WAL from WAL service and stores it in the repository.
• Page service - service that communicates with compute nodes and responds with pages from the repository.
• WAL redo - service that builds pages from base images and WAL records on Page service request.

Running local installation

1. Install build dependencies and other useful packages

On Ubuntu or Debian this set of packages should be sufficient to build the code:

apt install build-essential libtool libreadline-dev zlib1g-dev flex bison libseccomp-dev \
libssl-dev clang pkg-config libpq-dev

[Rust] 1.55 or later is also required.

To run the psql client, install the postgresql-client package or modify PATH and LD_LIBRARY_PATH to include tmp_install/bin and tmp_install/lib, respectively.

To run the integration tests (not required to use the code), install Python (3.7 or higher), and install python3 packages with pipenv using pipenv install in the project directory.

2. Build zenith and patched postgres

git clone --recursive https://github.com/zenithdb/zenith.git
cd zenith
make -j5

3. Start pageserver and postgres on top of it (should be called from repo root):

# Create repository in .zenith with proper paths to binaries and data
# Later that would be responsibility of a package install script
> ./target/debug/zenith init
initializing tenantid c03ba6b7ad4c5e9cf556f059ade44229
created initial timeline 5b014a9e41b4b63ce1a1febc04503636 timeline.lsn 0/169C3C8
created main branch
pageserver init succeeded

# start pageserver and safekeeper
> ./target/debug/zenith start
Starting pageserver at 'localhost:64000' in '.zenith'
Pageserver started
initializing for single for 7676
Starting safekeeper at 'localhost:5454' in '.zenith/safekeepers/single'
Safekeeper started

# start postgres compute node
> ./target/debug/zenith pg start main
Starting new postgres main on main...
Extracting base backup to create postgres instance: path=.zenith/pgdatadirs/tenants/c03ba6b7ad4c5e9cf556f059ade44229/main port=55432
Starting postgres node at 'host=127.0.0.1 port=55432 user=zenith_admin dbname=postgres'
waiting for server to start.... done
server started

# check list of running postgres instances
> ./target/debug/zenith pg list
BRANCH	ADDRESS		LSN		STATUS
main	127.0.0.1:55432	0/1609610	running

4. Now it is possible to connect to postgres and run some queries:

> psql -p55432 -h 127.0.0.1 -U zenith_admin postgres
postgres=# CREATE TABLE t(key int primary key, value text);
CREATE TABLE
postgres=# insert into t values(1,1);
INSERT 0 1
postgres=# select * from t;
 key | value
-----+-------
   1 | 1
(1 row)

5. And create branches and run postgres on them:

# create branch named migration_check
> ./target/debug/zenith branch migration_check main
Created branch 'migration_check' at 0/1609610

# check branches tree
> ./target/debug/zenith branch
 main
 ┗━ @0/1609610: migration_check

# start postgres on that branch
> ./target/debug/zenith pg start migration_check
Starting postgres node at 'host=127.0.0.1 port=55433 user=stas'
waiting for server to start.... done

# this new postgres instance will have all the data from 'main' postgres,
# but all modifications would not affect data in original postgres
> psql -p55433 -h 127.0.0.1 -U zenith_admin postgres
postgres=# select * from t;
 key | value
-----+-------
   1 | 1
(1 row)

postgres=# insert into t values(2,2);
INSERT 0 1

6. If you want to run tests afterwards (see below), you have to stop all the running the pageserver, safekeeper and postgres instances you have just started. You can stop them all with one command:

> ./target/debug/zenith stop

Running tests

git clone --recursive https://github.com/zenithdb/zenith.git
make # builds also postgres and installs it to ./tmp_install
cd test_runner
pytest

Documentation

Now we use README files to cover design ideas and overall architecture for each module and rustdoc style documentation comments. See also /docs/ a top-level overview of all available markdown documentation.

• /docs/sourcetree.md contains overview of source tree layout.

To view your rustdoc documentation in a browser, try running cargo doc --no-deps --open

Postgres-specific terms

Due to Zenith's very close relation with PostgreSQL internals, there are numerous specific terms used. Same applies to certain spelling: i.e. we use MB to denote 1024 * 1024 bytes, while MiB would be technically more correct, it's inconsistent with what PostgreSQL code and its documentation use.

To get more familiar with this aspect, refer to:

• Zenith glossary
• PostgreSQL glossary
• Other PostgreSQL documentation and sources (Zenith fork sources can be found here)

Join the development

• Read CONTRIBUTING.md to learn about project code style and practices.
• To get familiar with a source tree layout, use /docs/sourcetree.md.
• To learn more about PostgreSQL internals, check http://www.interdb.jp/pg/index.html