0bdbc39cb1
## Problem PR #4839 has already reduced the number of b-tree traversals and vec creations from 3 to 2, but as pointed out in https://github.com/neondatabase/neon/pull/4839#discussion_r1279167815 , we would ideally just traverse the b-tree once during compaction. Afer #4836, the two vecs created are one for the list of keys, lsns and sizes, and one for the list of `(key, lsn, value reference)`. However, they are not equal, as pointed out in https://github.com/neondatabase/neon/pull/4839#issuecomment-1660418012 and the following comment: the key vec creation combines multiple entries for which the lsn is changing but the key stays the same into one, with the size being the sum of the sub-sizes. In SQL, this would correspond to something like `SELECT key, lsn, SUM(size) FROM b_tree GROUP BY key;` and `SELECT key, lsn, val_ref FROM b_tree;`. Therefore, the join operation is non-trivial. ## Summary of changes This PR merges the two lists of keys and value references into one. It's not a trivial change and affects the size pattern of the resulting files, which is why this is in a separate PR from #4839 . The key vec is used in compaction for determining when to start a new layer file. The loop uses various thresholds to come to this conclusion, but the grouping via the key has led to the behaviour that regardless of the threshold, it only starts a new file when either a new key is encountered, or a new delta file. The new code now does the combination after the merging and sorting of the various keys from the delta files. This *mostly* does the same as the old code, except for a detail: with the grouping done on a per-delta-layer basis, the sorted and merged vec would still have multiple entries for multiple delta files, but now, we don't have an easy way to tell when a new input delta layer file is encountered, so we cannot create multiple entries on that basis easily. To prevent possibly infinite growth, our new grouping code compares the combined size with the threshold, and if it is exceeded, it cuts a new entry so that the downstream code can cut a new output file. Here, we perform a tradeoff however, as if the threshold is too small, we risk putting entries for the same key into multiple layer files, but if the threshold is too big, we can in some instances exceed the target size. Currently, we set the threshold to the target size, so in theory we would stay below or roughly at double the `target_file_size`. We also fix the way the size was calculated for the last key. The calculation was wrong and accounted for the old layer's btree, even though we already account for the overhead of the in-construction btree. Builds on top of #4839 .
Neon
Neon is a serverless open-source alternative to AWS Aurora Postgres. It separates storage and compute and substitutes the PostgreSQL storage layer by redistributing data across a cluster of nodes.
Quick start
Try the Neon Free Tier to create a serverless Postgres instance. Then connect to it with your preferred Postgres client (psql, dbeaver, etc) or use the online SQL Editor. See Connect from any application for connection instructions.
Alternatively, compile and run the project locally.
Architecture overview
A Neon installation consists of compute nodes and the Neon storage engine. Compute nodes are stateless PostgreSQL nodes backed by the Neon storage engine.
The Neon storage engine consists of two major components:
- Pageserver. Scalable storage backend for the compute nodes.
- Safekeepers. The safekeepers form a redundant WAL service that received WAL from the compute node, and stores it durably until it has been processed by the pageserver and uploaded to cloud storage.
See developer documentation in SUMMARY.md for more information.
Running local installation
Installing dependencies on Linux
- Install build dependencies and other applicable 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 cmake postgresql-client protobuf-compiler \
libcurl4-openssl-dev openssl python-poetry
- On Fedora, these packages are needed:
dnf install flex bison readline-devel zlib-devel openssl-devel \
libseccomp-devel perl clang cmake postgresql postgresql-contrib protobuf-compiler \
protobuf-devel libcurl-devel openssl poetry
- On Arch based systems, these packages are needed:
pacman -S base-devel readline zlib libseccomp openssl clang \
postgresql-libs cmake postgresql protobuf curl
Building Neon requires 3.15+ version of protoc (protobuf-compiler). If your distribution provides an older version, you can install a newer version from here.
# recommended approach from https://www.rust-lang.org/tools/install
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
Installing dependencies on macOS (12.3.1)
- Install XCode and dependencies
xcode-select --install
brew install protobuf openssl flex bison
# add openssl to PATH, required for ed25519 keys generation in neon_local
echo 'export PATH="$(brew --prefix openssl)/bin:$PATH"' >> ~/.zshrc
# recommended approach from https://www.rust-lang.org/tools/install
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
- Install PostgreSQL Client
# from https://stackoverflow.com/questions/44654216/correct-way-to-install-psql-without-full-postgres-on-macos
brew install libpq
brew link --force libpq
Rustc version
The project uses rust toolchain file to define the version it's built with in CI for testing and local builds.
This file is automatically picked up by rustup that installs (if absent) and uses the toolchain version pinned in the file.
rustup users who want to build with another toolchain can use rustup override command to set a specific toolchain for the project's directory.
non-rustup users most probably are not getting the same toolchain automatically from the file, so are responsible to manually verify their toolchain matches the version in the file. Newer rustc versions most probably will work fine, yet older ones might not be supported due to some new features used by the project or the crates.
Building on Linux
- Build neon and patched postgres
# Note: The path to the neon sources can not contain a space.
git clone --recursive https://github.com/neondatabase/neon.git
cd neon
# The preferred and default is to make a debug build. This will create a
# demonstrably slower build than a release build. For a release build,
# use "BUILD_TYPE=release make -j`nproc` -s"
# Remove -s for the verbose build log
make -j`nproc` -s
Building on OSX
- Build neon and patched postgres
# Note: The path to the neon sources can not contain a space.
git clone --recursive https://github.com/neondatabase/neon.git
cd neon
# The preferred and default is to make a debug build. This will create a
# demonstrably slower build than a release build. For a release build,
# use "BUILD_TYPE=release make -j`sysctl -n hw.logicalcpu` -s"
# Remove -s for the verbose build log
make -j`sysctl -n hw.logicalcpu` -s
Dependency installation notes
To run the psql client, install the postgresql-client package or modify PATH and LD_LIBRARY_PATH to include pg_install/bin and pg_install/lib, respectively.
To run the integration tests or Python scripts (not required to use the code), install
Python (3.9 or higher), and install python3 packages using ./scripts/pysync (requires poetry>=1.3) in the project directory.
Running neon database
- Start pageserver and postgres on top of it (should be called from repo root):
# Create repository in .neon with proper paths to binaries and data
# Later that would be responsibility of a package install script
> cargo neon init
Initializing pageserver node 1 at '127.0.0.1:64000' in ".neon"
# start pageserver, safekeeper, and broker for their intercommunication
> cargo neon start
Starting neon broker at 127.0.0.1:50051.
storage_broker started, pid: 2918372
Starting pageserver node 1 at '127.0.0.1:64000' in ".neon".
pageserver started, pid: 2918386
Starting safekeeper at '127.0.0.1:5454' in '.neon/safekeepers/sk1'.
safekeeper 1 started, pid: 2918437
# create initial tenant and use it as a default for every future neon_local invocation
> cargo neon tenant create --set-default
tenant 9ef87a5bf0d92544f6fafeeb3239695c successfully created on the pageserver
Created an initial timeline 'de200bd42b49cc1814412c7e592dd6e9' at Lsn 0/16B5A50 for tenant: 9ef87a5bf0d92544f6fafeeb3239695c
Setting tenant 9ef87a5bf0d92544f6fafeeb3239695c as a default one
# start postgres compute node
> cargo neon endpoint start main
Starting new endpoint main (PostgreSQL v14) on timeline de200bd42b49cc1814412c7e592dd6e9 ...
Starting postgres at 'postgresql://cloud_admin@127.0.0.1:55432/postgres'
# check list of running postgres instances
> cargo neon endpoint list
ENDPOINT ADDRESS TIMELINE BRANCH NAME LSN STATUS
main 127.0.0.1:55432 de200bd42b49cc1814412c7e592dd6e9 main 0/16B5BA8 running
- Now, it is possible to connect to postgres and run some queries:
> psql -p55432 -h 127.0.0.1 -U cloud_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)
- And create branches and run postgres on them:
# create branch named migration_check
> cargo neon timeline branch --branch-name migration_check
Created timeline 'b3b863fa45fa9e57e615f9f2d944e601' at Lsn 0/16F9A00 for tenant: 9ef87a5bf0d92544f6fafeeb3239695c. Ancestor timeline: 'main'
# check branches tree
> cargo neon timeline list
(L) main [de200bd42b49cc1814412c7e592dd6e9]
(L) ┗━ @0/16F9A00: migration_check [b3b863fa45fa9e57e615f9f2d944e601]
# start postgres on that branch
> cargo neon endpoint start migration_check --branch-name migration_check
Starting new endpoint migration_check (PostgreSQL v14) on timeline b3b863fa45fa9e57e615f9f2d944e601 ...
Starting postgres at 'postgresql://cloud_admin@127.0.0.1:55434/postgres'
# check the new list of running postgres instances
> cargo neon endpoint list
ENDPOINT ADDRESS TIMELINE BRANCH NAME LSN STATUS
main 127.0.0.1:55432 de200bd42b49cc1814412c7e592dd6e9 main 0/16F9A38 running
migration_check 127.0.0.1:55434 b3b863fa45fa9e57e615f9f2d944e601 migration_check 0/16F9A70 running
# this new postgres instance will have all the data from 'main' postgres,
# but all modifications would not affect data in original postgres
> psql -p55434 -h 127.0.0.1 -U cloud_admin postgres
postgres=# select * from t;
key | value
-----+-------
1 | 1
(1 row)
postgres=# insert into t values(2,2);
INSERT 0 1
# check that the new change doesn't affect the 'main' postgres
> psql -p55432 -h 127.0.0.1 -U cloud_admin postgres
postgres=# select * from t;
key | value
-----+-------
1 | 1
(1 row)
- If you want to run tests afterward (see below), you must stop all the running of the pageserver, safekeeper, and postgres instances you have just started. You can terminate them all with one command:
> cargo neon stop
Running tests
Ensure your dependencies are installed as described here.
git clone --recursive https://github.com/neondatabase/neon.git
CARGO_BUILD_FLAGS="--features=testing" make
./scripts/pytest
By default, this runs both debug and release modes, and all supported postgres versions. When testing locally, it is convenient to run just run one set of permutations, like this:
DEFAULT_PG_VERSION=15 BUILD_TYPE=release ./scripts/pytest
Documentation
docs Contains a top-level overview of all available markdown documentation.
- sourcetree.md contains overview of source tree layout.
To view your rustdoc documentation in a browser, try running cargo doc --no-deps --open
See also README files in some source directories, and rustdoc style documentation comments.
Other resources:
- SELECT 'Hello, World': Blog post by Nikita Shamgunov on the high level architecture
- Architecture decisions in Neon: Blog post by Heikki Linnakangas
- Neon: Serverless PostgreSQL!: Presentation on storage system by Heikki Linnakangas in the CMU Database Group seminar series
Postgres-specific terms
Due to Neon's very close relation with PostgreSQL internals, numerous specific terms are used. The 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:
- Neon glossary
- PostgreSQL glossary
- Other PostgreSQL documentation and sources (Neon 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 sourcetree.md.
- To learn more about PostgreSQL internals, check http://www.interdb.jp/pg/index.html