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‎contrib/mmts/README.md

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# pg_dtm
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### Design
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This repo implements distributed transaction manager using Snapshot Sharing mechanism. General concepts and alternative approaches described in postgres wiki https://wiki.postgresql.org/wiki/DTM.
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Backend-DTM protocol description can be found in [dtmd/README](dtmd/README).
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### Installation
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* Patch postgres using xtm.patch. After that build and install postgres in usual way.
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```bash
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cd ~/code/postgres
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patch -p1 < ~/code/pg_dtm/xtm.patch
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```
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* Install pg_dtm extension.
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```bash
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export PATH=/path/to/pgsql/bin/:$PATH
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cd ~/code/pg_dtm
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make && make install
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```
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* Run dtmd.
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```bash
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cd ~/code/pg_dtm/dtmd
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make
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mkdir /tmp/clog
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./bin/dtmd &
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```
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* To run something meaningful you need at leat two postgres instances. Also pg_dtm requires presense in ```shared_preload_libraries```.
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```bash
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initdb -D ./install/data1
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initdb -D ./install/data2
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echo "port = 5433" >> ./install/data2/postgresql.conf
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echo "shared_preload_libraries = 'pg_dtm'" >> ./install/data1/postgresql.conf
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echo "shared_preload_libraries = 'pg_dtm'" >> ./install/data2/postgresql.conf
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pg_ctl -D ./install/data1 -l ./install/data1/log start
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pg_ctl -D ./install/data2 -l ./install/data2/log start
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```
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#### Automatic provisioning
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For a cluster-wide deploy we use ansible, more details in tests/deploy_layouts. (Ansible instructions will be later)
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### Usage
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Now cluster is running and you can use global tx between two nodes. Let's connect to postgres instances at different ports:
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```sql
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create extension pg_dtm; -- node1
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create table accounts(user_id int, amount int); -- node1
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insert into accounts (select 2*generate_series(1,100)-1, 0); -- node1, odd user_id's
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create extension pg_dtm; -- node2
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create table accounts(user_id int, amount int); -- node2
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insert into accounts (select 2*generate_series(1,100), 0); -- node2, even user_id's
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select dtm_begin_transaction(); -- node1, returns global xid, e.g. 42
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select dtm_join_transaction(42); -- node2, join global tx
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begin; -- node1
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begin; -- node2
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update accounts set amount=amount-100 where user_id=1; -- node1, transfer money from user#1
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update accounts set amount=amount+100 where user_id=2; -- node2, to user#2
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commit; -- node1, blocks until second commit happend
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commit; -- node2
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```
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### Consistency testing
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To ensure consistency we use simple bank test: perform a lot of simultaneous transfers between accounts on different servers, while constantly checking total amount of money on all accounts. This test can be found in tests/perf.
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```bash
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> go run ./tests/perf/*
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-C value
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Connection string (repeat for multiple connections)
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-a int
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The number of bank accounts (default 100000)
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-b string
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Backend to use. Possible optinos: transfers, fdw, pgshard, readers. (default "transfers")
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-g Use DTM to keep global consistency
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-i Init database
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-l Use 'repeatable read' isolation level instead of 'read committed'
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-n int
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The number updates each writer (reader in case of Reades backend) performs (default 10000)
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-p Use parallel execs
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-r int
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The number of readers (default 1)
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-s int
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StartID. Script will update rows starting from this value
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-v Show progress and other stuff for mortals
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-w int
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The number of writers (default 8)
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```
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So previous installation can be initialized with:
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```
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go run ./tests/perf/*.go \
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-C "dbname=postgres port=5432" \
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-C "dbname=postgres port=5433" \
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-g -i
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```
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and tested with:
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```
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go run ./tests/perf/*.go \
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-C "dbname=postgres port=5432" \
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-C "dbname=postgres port=5433" \
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-g
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```
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### Using with postres_fdw.
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We also provide a patch, that enables support of global transactions with postres_fdw. After patching and installing postres_fdw it is possible to run same test via fdw usig key ```-b fdw```.
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### Using with pg_shard
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Citus Data have branch in their pg_shard repo, that interacts with transaction manager. https://github.com/citusdata/pg_shard/tree/transaction_manager_integration
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To use this feature one should have following line in postgresql.conf (or set it via GUC)
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```
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pg_shard.use_dtm_transactions = 1
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```
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# Postgres Multimaster
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## Testing
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The testing process involves multiple modules that perform different tasks. The
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modules and their APIs are listed below.
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### Modules
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#### `combineaux`
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Governs the whole testing process. Runs different workloads during different
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troubles.
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#### `stresseaux`
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Puts workloads against the database. Writes logs that are later used by
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`valideaux`.
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* `start(id, workload, cluster)` - starts a `workload` against the `cluster`
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and call it `id`.
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* `stop(id)` - stops a previously started workload called `id`.
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#### `starteaux`
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Manages the database nodes.
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* `deploy(driver, ...)` - deploys a cluster using the specified `driver` and
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other parameters specific to that driver. Returns a `cluster` instance that is
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used in other methods.
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* `cluster->up(id)` - adds a node named `id` to the `cluster`.
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* `cluster->down(id)` - removes a node named `id` from the `cluster`.
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* `cluster->drop(src, dst, ratio)` - drop `ratio` packets flowing from node
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`src` to node `dst`.
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* `cluster->delay(src, dst, msec)` - delay packets flowing from node `src` to
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node `dst` by `msec` milliseconds.
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#### `troubleaux`
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This is the troublemaker that messes with the network, nodes and time.
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* `cause(cluster, trouble, ...)` - causes the specified `trouble` in the
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specified `cluster` with some trouble-specific parameters.
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* `fix(cluster)` - fixes all troubles caused in the `cluster`.
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#### `valideaux`
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Validates the logs of stresseaux.
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#### `reporteaux`
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Generates reports on the test results. This is usually a table that with
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`trouble` vs `workload` axes.

‎contrib/mmts/Testeaux.pm

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package Testeaux;
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package combineaux
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{
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sub combine
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{
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my ($workloads, $troubles) = @_;
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my $cluster = starteaux->deploy('lxc');
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foreach my $workload (@$workloads)
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{
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foreach my $trouble (@$troubles)
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{
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print("run workload $workload during trouble $trouble\n");
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# FIXME: generate proper id instead of 'hello'
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stresseaux::start('hello', $workload, $cluster);
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# FIXME: add a time gap here
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troubleaux::cause($cluster, $trouble);
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# FIXME: add a time gap here
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stresseaux::stop('hello');
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troubleaux::fix($cluster);
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}
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}
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}
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}
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package stresseaux
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{
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sub start
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{
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my ($id, $workload, $cluster) = @_;
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print("start stress $id: workload $workload, cluster $cluster\n");
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# fixme: implement
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}
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sub stop
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{
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my $id = shift;
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print("stop stress $id\n");
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# FIXME: implement
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}
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}
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package starteaux
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{
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sub deploy
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{
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my ($class, $driver, @args) = @_;
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my $self = {};
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print("deploy cluster using driver $driver\n");
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# fixme: implement
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return bless $self, 'starteaux';
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}
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sub up
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{
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my ($self, $id) = @_;
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print("up node $id\n");
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# FIXME: implement
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}
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sub down
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{
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my ($self, $id = @_;
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print("down node $id\n");
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# FIXME: implement
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}
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sub drop
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{
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my ($self, $src, $dst, $ratio) = @_;
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print("drop $ratio packets from $src to $dst\n");
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# FIXME: implement
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}
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sub delay
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{
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my ($self, $src, $dst, $msec) = @_;
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print("delay packets from $src to $dst by $msec msec\n");
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# FIXME: implement
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}
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}
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1;

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