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Add documentation for autocompressor (#70)

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2
Cargo.lock generated
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@@ -1143,10 +1143,12 @@ dependencies = [
"indicatif",
"jemallocator",
"log",
"log-panics",
"openssl",
"postgres",
"postgres-openssl",
"pyo3",
"pyo3-log",
"rand",
"rayon",
"state-map",

2
Cargo.toml
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@@ -20,6 +20,8 @@ rayon = "1.3.0"
string_cache = "0.8.0"
env_logger = "0.9.0"
log = "0.4.14"
pyo3-log = "0.4.0"
log-panics = "2.0.0"
[dependencies.state-map]
git = "https://github.com/matrix-org/rust-matrix-state-map"

293
README.md
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@@ -1,47 +1,111 @@
# Compress Synapse State Tables
An experimental tool that reads in the rows from `state_groups_state` and
`state_group_edges` tables for a particular room and calculates the changes that
could be made that (hopefully) will significantly reduce the number of rows.
This workspace contains experimental tools that attempt to reduce the number of
rows in the `state_groups_state` table inside of a Synapse Postgresql database.
This tool currently *does not* write to the database in any way, so should be
# Automated tool: auto_compressor
## Introduction:
This tool is significantly more simple to use than the manual tool (described below).
It scans through all of the rows in the `state_groups` database table from the start. When
it finds a group that hasn't been compressed, it runs the compressor for a while on that
group's room, saving where it got up to. After compressing a number of these chunks it stops,
saving where it got up to for the next run of the `auto_compressor`.
It creates three extra tables in the database: `state_compressor_state` which stores the
information needed to stop and start the compressor for each room, `state_compressor_progress`
which stores the most recently compressed state group for each room and `state_compressor_total_progress`
which stores how far through the `state_groups` table the compressor has scanned.
The tool can be run manually when you are running out of space, or be scheduled to run
periodically.
The output from the auto_compressor will be sent to `auto_compressor.log` (in the directory
that the compressor is run from).
## Building
This tool requires `cargo` to be installed. See https://www.rust-lang.org/tools/install
for instructions on how to do this.
To build `auto_compressor`, clone this repository and navigate to the `autocompressor/`
subdirectory. Then execute `cargo build`.
This will create an executable and store it in `auto_compressor/target/debug/auto_compressor`.
## Example usage
```
$ auto_compressor -p postgresql://user:pass@localhost/synapse -c 500 -n 100
```
## Running Options
- -p [POSTGRES_LOCATION] **Required**
The configuration for connecting to the Postgres database. This should be of the form
`"postgresql://username:password@mydomain.com/database"` or a key-value pair
string: `"user=username password=password dbname=database host=mydomain.com"`
See https://docs.rs/tokio-postgres/0.7.2/tokio_postgres/config/struct.Config.html
for the full details.
- -c [CHUNK_SIZE] **Required**
The number of state groups to work on at once. All of the entries from state_groups_state are
requested from the database for state groups that are worked on. Therefore small chunk
sizes may be needed on machines with low memory. Note: if the compressor fails to find
space savings on the chunk as a whole (which may well happen in rooms with lots of backfill
in) then the entire chunk is skipped.
- -n [CHUNKS_TO_COMPRESS] **Required**
*CHUNKS_TO_COMPRESS* chunks of size *CHUNK_SIZE* will be compressed. The higher this
number is set to, the longer the compressor will run for.
- -d [LEVELS]
Sizes of each new level in the compression algorithm, as a comma-separated list.
The first entry in the list is for the lowest, most granular level, with each
subsequent entry being for the next highest level. The number of entries in the
list determines the number of levels that will be used. The sum of the sizes of
the levels affects the performance of fetching the state from the database, as the
sum of the sizes is the upper bound on the number of iterations needed to fetch a
given set of state. [defaults to "100,50,25"]
## Scheduling the compressor
The automatic tool may put some strain on the database, so it might be best to schedule
it to run at a quiet time for the server. This could be done by creating an executable
script and scheduling it with something like
[cron](https://www.man7.org/linux/man-pages/man1/crontab.1.html).
# Manual tool: synapse_compress_state
## Introduction
A manual tool that reads in the rows from `state_groups_state` and `state_group_edges`
tables for a specified room and calculates the changes that could be made that
(hopefully) will significantly reduce the number of rows.
This tool currently *does not* write to the database by default, so should be
safe to run. If the `-o` option is specified then SQL will be written to the
given file that would change the tables to match the calculated state. (Note
that if `-t` is given then each change to a particular state group is wrapped
in a transaction).
in a transaction). If you do wish to send the changes to the database automatically
then the `-c` flag can be set.
The SQL generated by the `-o` option is safe to apply against the database with
Synapse running. This is because the `state_groups` and `state_groups_state`
tables are append-only: once written to the database, they are never modified.
There is therefore no danger of a modification racing against a running synapse.
Further, this script makes its changes within atomic transactions, and each
transaction should not affect the results from any of the queries that synapse
performs.
The SQL generated is safe to apply against the database with Synapse running.
This is because the `state_groups` and `state_groups_state` tables are append-only:
once written to the database, they are never modified. There is therefore no danger
of a modification racing against a running Synapse. Further, this script makes its
changes within atomic transactions, and each transaction should not affect the results
from any of the queries that Synapse performs.
The tool will also ensure that the generated state deltas do give the same state
as the existing state deltas before generating any SQL.
## Algorithm
## Building
The algorithm works by attempting to create a tree of deltas, produced by
appending state groups to different "levels". Each level has a maximum size, where
each state group is appended to the lowest level that is not full.
This tool requires `cargo` to be installed. See https://www.rust-lang.org/tools/install
for instructions on how to do this.
This produces a graph that looks approximately like the following, in the case
of having two levels with the bottom level (L1) having a maximum size of 3:
```
L2 <-------------------- L2 <---------- ...
^--- L1 <--- L1 <--- L1 ^--- L1 <--- L1 <--- L1
```
The sizes and number of levels used can be controlled via `-l`, and defaults to 3
levels of sizes 100, 50 and 25.
**Note**: Increasing the sum of the sizes of levels will increase the time it
takes for to query the full state of a given state group. By default Synapse
attempts to keep this below 100.
To build `synapse_compress_state`, clone this repository and then execute `cargo build`.
This will create an executable and store it in `target/debug/synapse_compress_state`.
## Example usage
@@ -64,92 +128,65 @@ $ psql synapse < out.data
## Running Options
- -p [URL] **Required**
The url for connecting to the postgres database. This should be of the form
"postgresql://username:password@mydomain.com/database"
- -p [POSTGRES_LOCATION] **Required**
The configuration for connecting to the Postgres database. This should be of the form
`"postgresql://username:password@mydomain.com/database"` or a key-value pair
string: `"user=username password=password dbname=database host=mydomain.com"`
See https://docs.rs/tokio-postgres/0.7.2/tokio_postgres/config/struct.Config.html
for the full details.
- -r [ROOM_ID] **Required**
The room to process. This is the value found in the `rooms` table of the database
not the common name for the room - is should look like: "!wOlkWNmgkAZFxbTaqj:matrix.org"
The room to process (this is the value found in the `rooms` table of the database
not the common name for the room - it should look like: "!wOlkWNmgkAZFxbTaqj:matrix.org".
- -b [MIN_STATE_GROUP]
The state group to start processing from (non inclusive)
The state group to start processing from (non-inclusive).
- -n [GROUPS_TO_COMPRESS]
How many groups to load into memory to compress (starting
from the 1st group in the room or the group specified by -s)
from the 1st group in the room or the group specified by -b).
- -l [LEVELS]
Sizes of each new level in the compression algorithm, as a comma separated list.
Sizes of each new level in the compression algorithm, as a comma-separated list.
The first entry in the list is for the lowest, most granular level, with each
subsequent entry being for the next highest level. The number of entries in the
list determines the number of levels that will be used. The sum of the sizes of
the levels effect the performance of fetching the state from the database, as the
sum of the sizes is the upper bound on number of iterations needed to fetch a
given set of state. [default's to 100,50,25]
the levels affects the performance of fetching the state from the database, as the
sum of the sizes is the upper bound on the number of iterations needed to fetch a
given set of state. [defaults to "100,50,25"]
- -m [COUNT]
If the compressor cannot save this many rows from the database then it will stop early
If the compressor cannot save this many rows from the database then it will stop early.
- -s [MAX_STATE_GROUP]
If a max_state_group is specified then only state groups with id's lower than this number are able to be
compressed.
If a max_state_group is specified then only state groups with id's lower than this
number can be compressed.
- -o [FILE]
File to output the SQL transactions to (for later running on the database)
File to output the SQL transactions to (for later running on the database).
- -t
If this flag is set then then each change to a particular state group is wrapped in a transaction. This should be done if you wish to apply the changes while synapse is still running.
If this flag is set then each change to a particular state group is wrapped in a
transaction. This should be done if you wish to apply the changes while synapse is
still running.
- -c
If this flag is set then the changes the compressor makes will be committed to the
database. This should be safe to use while synapse is running as it wraps the changes
to every state group in it's own transaction (as if the transaction flag was set).
- -g
If this flag is set then output the node and edge information for the state_group
directed graph built up from the predecessor state_group links. These can be looked
at in something like Gephi (https://gephi.org)
at in something like Gephi (https://gephi.org).
- -c
If this flag is set then the changes the compressor makes will be committed to the
database. This should be safe to use while synapse is running as it assumes by default
that the transactions flag is set
## Using as python library
# Running tests
The compressor can also be built into a python library as it uses PyO3. It can be
built and installed into the current virtual environment by running `maturin develop`
There are integration tests for these tools stored in `compressor_integration_tests/`.
All the same running options are available, see the comments in the Config struct
in lib.rs for the names of each argument. All arguments other than `db_url` and `room_id`
are optional.
The following code does exactly the same as the command-line example from above:
```
import synapse_compress_state as comp
comp.run_compression(
db_url="postgresql://localhost/synapse",
room_id="!some_room:example.com",
output_file="out.sql",
transactions=True
)
```
Note: since this library uses Jemalloc, you might get an error of the form:
```
ImportError: /[LONG_PATH]/synapse_compress_state.abi3.so: cannot allocate memory in static TLS block
```
If this happens then try running the following:
```
LD_PATH=/[LONG_PATH]/synapse_compress_state.abi3.so ./my_python_script
```
Or just try disabling jemalloc:
```
$ maturin develop --cargo-extra-args="--no-default-features"
```
## Running tests
There are integration tests for these tool stored in `compressor_integration_tests/`
To run the integration tests, you first need to start up a postgres database
for the libary to talk to. There is a docker-compose file that sets one up
To run the integration tests, you first need to start up a Postgres database
for the library to talk to. There is a docker-compose file that sets one up
with all of the correct tables. The tests can therefore be run as follows:
```
@@ -159,5 +196,81 @@ $ cargo test --workspace
$ docker-compose down
```
Note, any output from these tests goes into `compressor_integration_tests/tmp/` so if this
directory doesn't already exist then you will need to create it.
# Using the synapse_compress_state library
If you want to use the compressor in another project, it is recomended that you
use jemalloc `https://github.com/gnzlbg/jemallocator`.
To prevent the progress bars from being shown, use the `no-progress-bars` feature.
(See `auto_compressor/Cargo.toml` for an example)
# Troubleshooting
## Connecting to database
### From local machine
If you setup Synapse using the instructions on https://matrix-org.github.io/synapse/latest/postgres.html
you should have a username and password to use to login to the postgres database. To run the compressor
from the machine where Postgres is running, the url will be the following:
`postgresql://synapse_user:synapse_password@localhost/synapse`
### From remote machine
If you wish to connect from a different machine, you'll need to edit your Postgres settings to allow
remote connections. This requires updating the
[`pg_hba.conf`](https://www.postgresql.org/docs/current/auth-pg-hba-conf.html) and the `listen_addresses`
setting in [`postgresql.conf`](https://www.postgresql.org/docs/current/runtime-config-connection.html)
## Printing debugging logs
The amount of output the tools produce can be altered by setting the RUST_LOG
environment variable to something.
To get more logs when running the auto_compressor tool try the following:
```
$ RUST_LOG=debug auto_compressor -p postgresql://user:pass@localhost/synapse -c 50 -n 100
```
If you want to suppress all the debugging info you are getting from the
Postgres client then try:
```
RUST_LOG=auto_compressor=debug,synapse_compress_state=debug auto_compressor [etc.]
```
This will only print the debugging information from those two packages. For more info see
https://docs.rs/env_logger/0.9.0/env_logger/.
## Building difficulties
Building the `openssl-sys` dependency crate requires OpenSSL development tools to be installed,
and building on Linux will also require `pkg-config`
This can be done on Ubuntu with: `$ apt-get install libssl-dev pkg-config`
Note that building requires quite a lot of memory and out-of-memory errors might not be
obvious. It's recomended you only build these tools on machines with at least 2GB of RAM.
## Auto Compressor skips chunks when running on already compressed room
If you have used the compressor before, with certain config options, the automatic tool will
produce lots of warnings of the form: `The compressor tried to increase the number of rows in ...`
To fix this, ensure that the chunk_size is set to at least the L1 level size (so if the level
sizes are "100,50,25" then the chunk_size should be at least 100).
Note: if the level sizes being used when rerunning are different to when run previously
this might lead to less efficient compression and thus chunks being skipped, but this shouldn't
be a large problem.
## Compressor is trying to increase the number of rows
Backfilling can lead to issues with compression. The auto_compressor will
skip chunks it can't reduce the size of and so this should help jump over the backfilled
state_groups. Lots of state resolution might also impact the ability to use the compressor.
To examine the state_group hierarchy run the manual tool on a room with the `-g` option
and look at the graphs.

17
auto_compressor/src/main.rs
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@@ -65,11 +65,15 @@ fn main() {
.arg(
Arg::with_name("postgres-url")
.short("p")
.value_name("URL")
.help("The url for connecting to the postgres database.")
.value_name("POSTGRES_LOCATION")
.help("The configruation for connecting to the postgres database.")
.long_help(concat!(
"The url for connecting to the postgres database.This should be of",
" the form \"postgresql://username:password@mydomain.com/database\""))
"The configuration for connecting to the Postgres database. This should be of the form ",
r#""postgresql://username:password@mydomain.com/database" or a key-value pair "#,
r#"string: "user=username password=password dbname=database host=mydomain.com" "#,
"See https://docs.rs/tokio-postgres/0.7.2/tokio_postgres/config/struct.Config.html ",
"for the full details."
))
.takes_value(true)
.required(true),
).arg(
@@ -111,7 +115,10 @@ fn main() {
.short("n")
.value_name("CHUNKS_TO_COMPRESS")
.help("The number of chunks to compress")
.long_help("This many chunks of the database will be compressed ")
.long_help(concat!(
"This many chunks of the database will be compressed. The higher this number is set to, ",
"the longer the compressor will run for."
))
.takes_value(true)
.required(true),
).get_matches();

2
compressor_integration_tests/src/lib.rs
View File

@@ -358,7 +358,7 @@ fn functions_are_self_consistent() {
pub fn setup_logger() {
// setup the logger for the auto_compressor
// The default can be overwritten with RUST_LOG
// see the README for more information <--- TODO
// see the README for more information
if env::var("RUST_LOG").is_err() {
let mut log_builder = env_logger::builder();
// set is_test(true) so that the output is hidden by cargo test (unless the test fails)

107
docs/algorithm.md Normal file
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@@ -0,0 +1,107 @@
# Compression algorithm
## What is state?
State is things like who is in a room, what the room topic/name is, who has
what privilege levels etc. Synapse keeps track of it for various reasons such as
spotting invalid events (e.g. ones sent by banned users) and providing room membership
information to clients.
## What is a state group?
Synapse needs to keep track of the state at the moment of each event. A state group
corresponds to a unique state. The database table `event_to_state_groups` keeps track
of the mapping from event ids to state group ids.
Consider the following simplified example:
```
State group id | State
_____________________________________________
1 | Alice in room
2 | Alice in room, Bob in room
3 | Bob in room
Event id | What the event was
______________________________________
1 | Alice sends a message
3 | Bob joins the room
4 | Bob sends a message
5 | Alice leaves the room
6 | Bob sends a message
Event id | State group id
_________________________
1 | 1
2 | 1
3 | 2
4 | 2
5 | 3
6 | 3
```
## What are deltas and predecessors?
When a new state event happens (e.g. Bob joins the room) a new state group is created.
BUT instead of copying all of the state from the previous state group, we just store
the change from the previous group (saving on lots of storage space!). The difference
from the previous state group is called the "delta".
So for the previous example, we would have the following (Note only rows 1 and 2 will
make sense at this point):
```
State group id | Previous state group id | Delta
____________________________________________________________
1 | NONE | Alice in room
2 | 1 | Bob in room
3 | NONE | Bob in room
```
So why is state group 3's previous state group NONE and not 2? Well, the way that deltas
work in Synapse is that they can only add in new state or overwrite old state, but they
cannot remove it. (So if the room topic is changed then that is just overwriting state,
but removing Alice from the room is neither an addition nor an overwriting). If it is
impossible to find a delta, then you just start from scratch again with a "snapshot" of
the entire state.
(NOTE this is not documentation on how synapse handles leaving rooms but is purely for illustrative
purposes)
The state of a state group is worked out by following the previous state group's and adding
together all of the deltas (with the most recent taking precedence).
The mapping from state group to previous state group takes place in `state_group_edges`
and the deltas are stored in `state_groups_state`.
## What are we compressing then?
In order to speed up the conversion from state group id to state, there is a limit of 100
hops set by synapse (that is: we will only ever have to look up the deltas for a maximum of
100 state groups). It does this by taking another "snapshot" every 100 state groups.
However, it is these snapshots that take up the bulk of the storage in a synapse database,
so we want to find a way to reduce the number of them without dramatically increasing the
maximum number of hops needed to do lookups.
## Compression Algorithm
The algorithm works by attempting to create a *tree* of deltas, produced by
appending state groups to different "levels". Each level has a maximum size, where
each state group is appended to the lowest level that is not full. This tool calls a
state group "compressed" once it has been added to
one of these levels.
This produces a graph that looks approximately like the following, in the case
of having two levels with the bottom level (L1) having a maximum size of 3:
```
L2 <-------------------- L2 <---------- ...
^--- L1 <--- L1 <--- L1 ^--- L1 <--- L1 <--- L1
NOTE: A <--- B means that state group B's predecessor is A
```
The structure that synapse creates by default would be equivalent to having one level with
a maximum length of 100.
**Note**: Increasing the sum of the sizes of levels will increase the time it
takes to query the full state of a given state group.

54
docs/python.md Normal file
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@@ -0,0 +1,54 @@
# Running the compressor tools from python
Both the automatic and manual tools use PyO3 to allow the compressor
to be run from Python.
To see any output from the tools, logging must be setup in Python before
the compressor is run.
## Setting things up
1. Create a virtual environment in the place you want to use the compressor from
(if it doesn't already exist)
`$ virtualenv -p python3 venv`
2. Activate the virtual environment and install `maturin` (if you haven't already)
`$ source venv/bin/activate`
`$ pip install maturin`
3. Navigate to the correct location
For the automatic tool:
`$ cd /home/synapse/rust-synapse-compress-state/auto_compressor`
For the manual tool:
`$ cd /home/synapse/rust-synapse-compress-state`
3. Build and install the library
`$ maturin develop`
This will install the relevant compressor tool into the activated virtual environment.
## Automatic tool example:
```python
import auto_compressor
auto_compressor.compress_state_events_table(
db_url="postgresql://localhost/synapse",
chunk_size=500,
default_levels="100,50,25",
number_of_chunks=100
)
```
# Manual tool example:
```python
import synapse_compress_state
synapse_compress_state.run_compression(
db_url="postgresql://localhost/synapse",
room_id="!some_room:example.com",
output_file="out.sql",
transactions=True
)
```

24
src/lib.rs
View File

@@ -20,7 +20,7 @@
// of arguments - this hopefully doesn't make the code unclear
// #[allow(clippy::too_many_arguments)] is therefore used around some functions
use log::{info, warn};
use log::{info, warn, LevelFilter};
use pyo3::{exceptions, prelude::*};
use clap::{crate_authors, crate_description, crate_name, crate_version, value_t, App, Arg};
@@ -121,11 +121,15 @@ impl Config {
.arg(
Arg::with_name("postgres-url")
.short("p")
.value_name("URL")
.help("The url for connecting to the postgres database.")
.value_name("POSTGRES_LOCATION")
.help("The configruation for connecting to the postgres database.")
.long_help(concat!(
"The url for connecting to the postgres database.This should be of",
" the form \"postgresql://username:password@mydomain.com/database\""))
"The configuration for connecting to the Postgres database. This should be of the form ",
r#""postgresql://username:password@mydomain.com/database" or a key-value pair "#,
r#"string: "user=username password=password dbname=database host=mydomain.com" "#,
"See https://docs.rs/tokio-postgres/0.7.2/tokio_postgres/config/struct.Config.html ",
"for the full details."
))
.takes_value(true)
.required(true),
).arg(
@@ -781,6 +785,16 @@ fn run_compression(
/// Python module - "import synapse_compress_state" to use
#[pymodule]
fn synapse_compress_state(_py: Python, m: &PyModule) -> PyResult<()> {
let _ = pyo3_log::Logger::default()
// don't send out anything lower than a warning from other crates
.filter(LevelFilter::Warn)
// don't log warnings from synapse_compress_state, the auto_compressor handles these
// situations and provides better log messages
.filter_target("synapse_compress_state".to_owned(), LevelFilter::Debug)
.install();
// ensure any panics produce error messages in the log
log_panics::init();
m.add_function(wrap_pyfunction!(run_compression, m)?)?;
Ok(())
}

2
src/main.rs
View File

@@ -29,7 +29,7 @@ use synapse_compress_state as comp_state;
fn main() {
// setup the logger
// The default can be overwritten with RUST_LOG
// see the README for more information <---- TODO
// see the README for more information
if env::var("RUST_LOG").is_err() {
let mut log_builder = env_logger::builder();
// Only output the log message (and not the prefixed timestamp etc.)