OBJS = multimaster.o raftable.o arbiter.o bytebuf.o bgwpool.o pglogical_output.o pglogical_proto.o pglogical_receiver.o pglogical_apply.o pglogical_hooks.o pglogical_config.o pglogical_relid_map.o ddd.o bkb.o

PG_CPPFLAGS = -I$(libpq_srcdir) -DUSE_PGLOGICAL_OUTPUT

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.

Backend-DTM protocol description can be found in [dtmd/README](dtmd/README).

* Patch postgres using xtm.patch. After that build and install postgres in usual way.

cd ~/code/postgres

patch -p1 < ~/code/pg_dtm/xtm.patch

* Install pg_dtm extension.

export PATH=/path/to/pgsql/bin/:$PATH

cd ~/code/pg_dtm

make && make install

* Run dtmd.

cd ~/code/pg_dtm/dtmd

make

mkdir /tmp/clog

./bin/dtmd &

* To run something meaningful you need at leat two postgres instances. Also pg_dtm requires presense in ```shared_preload_libraries```.

initdb -D ./install/data1

initdb -D ./install/data2

echo "port = 5433" >> ./install/data2/postgresql.conf

echo "shared_preload_libraries = 'pg_dtm'" >> ./install/data1/postgresql.conf

echo "shared_preload_libraries = 'pg_dtm'" >> ./install/data2/postgresql.conf

pg_ctl -D ./install/data1 -l ./install/data1/log start

pg_ctl -D ./install/data2 -l ./install/data2/log start

For a cluster-wide deploy we use ansible, more details in tests/deploy_layouts. (Ansible instructions will be later)

Now cluster is running and you can use global tx between two nodes. Let's connect to postgres instances at different ports:

create extension pg_dtm; -- node1

create table accounts(user_id int, amount int); -- node1

insert into accounts (select 2*generate_series(1,100)-1, 0); -- node1, odd user_id's

create extension pg_dtm; -- node2

create table accounts(user_id int, amount int); -- node2

insert into accounts (select 2*generate_series(1,100), 0); -- node2, even user_id's

select dtm_begin_transaction(); -- node1, returns global xid, e.g. 42

select dtm_join_transaction(42); -- node2, join global tx

begin; -- node1

begin; -- node2

update accounts set amount=amount-100 where user_id=1; -- node1, transfer money from user#1

update accounts set amount=amount+100 where user_id=2; -- node2, to user#2

commit; -- node1, blocks until second commit happend

commit; -- node2

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.

> go run ./tests/perf/*

-C value

Connection string (repeat for multiple connections)

-a int

The number of bank accounts (default 100000)

-b string

Backend to use. Possible optinos: transfers, fdw, pgshard, readers. (default "transfers")

-g Use DTM to keep global consistency

-i Init database

-l Use 'repeatable read' isolation level instead of 'read committed'

-n int

The number updates each writer (reader in case of Reades backend) performs (default 10000)

-p Use parallel execs

-r int

The number of readers (default 1)

-s int

StartID. Script will update rows starting from this value

-v Show progress and other stuff for mortals

-w int

The number of writers (default 8)

go run ./tests/perf/*.go \

-C "dbname=postgres port=5432" \

-C "dbname=postgres port=5433" \

-g -i

go run ./tests/perf/*.go \

-C "dbname=postgres port=5432" \

-C "dbname=postgres port=5433" \

-g

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```.

pg_shard.use_dtm_transactions = 1