d1d2d5ce69
There was no guarantee that the SELECT FOR KEY SHARE queries actually
run in parallel. With unlucky timing, one query might finish before
the next one starts, so that the server doesn't need to create a
multixact. I got a failure like that on the CI:
batch_others/test_multixact.py:56: in test_multixact
assert(int(next_multixact_id) > int(next_multixact_id_old))
E AssertionError: assert 1 > 1
E + where 1 = int('1')
E + and 1 = int('1')
This could be reproduced by adding a random sleep in the runQuery
function, to make each query run at different times.
To fix, keep the transactions open after running the queries, so that
they will surely be open concurrently. With that, we can run the
queries serially, and don't need the 'multiprocessing' module anymore.
Fixes https://github.com/zenithdb/zenith/issues/196
Zenith
Zenith substitutes PostgreSQL storage layer and redistributes data across a cluster of nodes
Running local installation
- 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 \
libxml2-dev libcurl4-openssl-dev libssl-dev clang
Rust 1.48 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 (3.6 or higher), and install python3 packages with pip (called pip3 on some systems):
pip install pytest psycopg2
- Build zenith and patched postgres
git clone --recursive https://github.com/libzenith/zenith.git
cd zenith
make -j5
- 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
<...>
new zenith repository was created in .zenith
# start pageserver
> ./target/debug/zenith start
Starting pageserver at '127.0.0.1:64000' in .zenith
Pageserver started
# start postgres on top on the pageserver
> ./target/debug/zenith pg start main
Starting postgres node at 'host=127.0.0.1 port=55432 user=stas'
waiting for server to start.... done
# check list of running postgres instances
> ./target/debug/zenith pg list
BRANCH ADDRESS LSN STATUS
main 127.0.0.1:55432 0/1609610 running
- Now it is possible to connect to postgres and run some queries:
> psql -p55432 -h 127.0.0.1 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)
- 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 postgres
postgres=# select * from t;
key | value
-----+-------
1 | 1
(1 row)
postgres=# insert into t values(2,2);
INSERT 0 1
Running tests
git clone --recursive https://github.com/libzenith/zenith.git
make # builds also postgres and installs it to ./tmp_install
cd test_runner
pytest
Source tree layout
/walkeeper:
WAL safekeeper. Written in Rust.
/pageserver:
Page Server. Written in Rust.
Depends on the modified 'postgres' binary for WAL redo.
/vendor/postgres:
PostgreSQL source tree, with the modifications needed for Zenith.
/vendor/postgres/src/bin/safekeeper:
Extension (safekeeper_proxy) that runs in the compute node, and connects to the WAL safekeepers and streams the WAL
/test_runner:
Integration tests, written in Python using the pytest framework.