gem-hunterLogical Replication extension for PostgreSQL 17, 16, 15, 14, 13, 12, 11, 10, 9.6, 9.5, 9.4 (Postgres), providing much faster replication than Slony, Bucardo or Londiste, as well as cross-version upgrades.
The pglogical 2 extension provides logical streaming replication for PostgreSQL, using a publish/subscribe model. It is based on technology developed as part of the BDR project (http://2ndquadrant.com/BDR).
While pglogical is actively maintained, EnterpriseDB (which acquired 2ndQuadrant in 2020) focuses new feature development on a descendant of pglogical: Postgres Distributed. Postgres Distributed introduced new features such as DDL replication, write leaders, parallel apply, and more.
We use the following terms to describe data streams between nodes, deliberately reused from the earlier Slony technology:
pglogical is utilising the latest in-core features, so we have these version restrictions:
Use cases supported are:
Architectural details:
To use pglogical the provider and subscriber must be running PostgreSQL 9.4 or newer.
The pglogical extension must be installed on both provider and subscriber.
You must CREATE EXTENSION pglogical on both.
Tables on the provider and subscriber must have the same names and be in the same schema. Future revisions may add mapping features.
Tables on the provider and subscriber must have the same columns, with the same
data types in each column. CHECK constraints, NOT NULL constraints, etc., must
be the same or weaker (more permissive) on the subscriber than the provider.
Tables must have the same PRIMARY KEYs. It is not recommended to add additional
UNIQUE constraints other than the PRIMARY KEY (see below).
Some additional requirements are covered in Limitations and Restrictions.
pglogical is available as RPMs via yum for Fedora, CentOS, & RHEL, and as DEBs via apt for Debian and Ubuntu, or as source code here. Please see below for instructions on installing from source.
The instructions below are valid for Red Hat family of operating systems (RHEL, CentOS, Fedora). Pre-Requisites
These RPMs all require the PGDG PostgreSQL releases from http://yum.postgresql.org/. You cannot use them with stock PostgreSQL releases included in Fedora and RHEL. If you don’t have PostgreSQL already:
yum install postgresql95-server postgresql95-contribyum install postgresql96-server postgresql96-contribyum install postgresql10-server postgresql10-contribyum install postgresql11-server postgresql11-contribyum install postgresql12-server postgresql12-contribyum install postgresql13-server postgresql13-contribyum install postgresql14-server postgresql14-contribyum install postgresql15-server postgresql15-contribyum install postgresql16-server postgresql16-contribyum install postgresql17-server postgresql17-contribyum install postgresql18-server postgresql18-contribyum install postgresql19-server postgresql19-contribYou can proceed to install pglogical for your PostgreSQL version:
yum install pglogical_95yum install pglogical_96yum install pglogical_10yum install pglogical_11yum install pglogical_12yum install pglogical_13yum install pglogical_14yum install pglogical_15yum install pglogical_16yum install pglogical_17yum install pglogical_18yum install pglogical_19The instructions below are valid for Debian and all Linux flavors based on Debian (e.g. Ubuntu).
sudo apt-get install postgresql-9.5sudo apt-get install postgresql-9.6sudo apt-get install postgresql-10sudo apt-get install postgresql-11sudo apt-get install postgresql-12sudo apt-get install postgresql-13sudo apt-get install postgresql-14sudo apt-get install postgresql-15sudo apt-get install postgresql-16sudo apt-get install postgresql-17sudo apt-get install postgresql-18sudo apt-get install postgresql-19Once pre-requisites are complete, installing pglogical is simply a matter of executing the following for your version of PostgreSQL:
sudo apt-get install postgresql-9.5-pglogicalsudo apt-get install postgresql-9.6-pglogicalsudo apt-get install postgresql-10-pglogicalsudo apt-get install postgresql-11-pglogicalsudo apt-get install postgresql-12-pglogicalsudo apt-get install postgresql-13-pglogicalsudo apt-get install postgresql-14-pglogicalsudo apt-get install postgresql-15-pglogicalsudo apt-get install postgresql-16-pglogicalsudo apt-get install postgresql-17-pglogicalsudo apt-get install postgresql-18-pglogicalsudo apt-get install postgresql-19-pglogicalSource code installs are the same as for any other PostgreSQL extension built using PGXS.
Make sure the directory containing pg_config from the PostgreSQL release is
listed in your PATH environment variable. You might have to install a -dev
or -devel package for your PostgreSQL release from your package manager if
you don't have pg_config.
Then run make to compile, and make install to
install. You might need to use sudo for the install step.
e.g. for a typical Fedora or RHEL 9 install, assuming you're using the yum.postgresql.org packages for PostgreSQL:
sudo dnf install postgresql19-devel
PATH=/usr/pgsql-19/bin:$PATH make clean all
sudo PATH=/usr/pgsql-19/bin:$PATH make install
This section describes basic usage of the pglogical replication extension.
First the PostgreSQL server has to be properly configured to support logical decoding:
wal_level = 'logical'
max_worker_processes = 10 # one per database needed on provider node
# one per node needed on subscriber node
max_replication_slots = 10 # one per node needed on provider node
max_wal_senders = 10 # one per node needed on provider node
shared_preload_libraries = 'pglogical'
If you are using PostgreSQL 9.5+ (this won't work on 9.4) and want to handle conflict resolution with last/first update wins (see Conflicts), you can add this additional option to postgresql.conf:
track_commit_timestamp = on # needed for last/first update wins conflict resolution
# property available in PostgreSQL 9.5+
pg_hba.conf has to allow logical replication connections from
localhost. Up until PostgreSQL 9.6, logical replication connections
are managed using the replication keyword in pg_hba.conf. In
PostgreSQL 10 and later, logical replication connections are treated
by pg_hba.conf as regular connections to the provider database.
Next the pglogical extension has to be installed on all nodes:
CREATE EXTENSION pglogical;
If using PostgreSQL 9.4, then the pglogical_origin extension
also has to be installed on that node:
CREATE EXTENSION pglogical_origin;
Now create the provider node:
SELECT pglogical.create_node(
node_name := 'provider1',
dsn := 'host=providerhost port=5432 dbname=db'
);
Add all tables in public schema to the default replication set.
SELECT pglogical.replication_set_add_all_tables('default', ARRAY['public']);
Optionally you can also create additional replication sets and add tables to them (see Replication sets).
It's usually better to create replication sets before subscribing so that all tables are synchronized during initial replication setup in a single initial transaction. However, users of bigger databases may instead wish to create them incrementally for better control.
Once the provider node is setup, subscribers can be subscribed to it. First the subscriber node must be created:
SELECT pglogical.create_node(
node_name := 'subscriber1',
dsn := 'host=thishost port=5432 dbname=db'
);
And finally on the subscriber node you can create the subscription which will start synchronization and replication process in the background:
SELECT pglogical.create_subscription(
subscription_name := 'subscription1',
provider_dsn := 'host=providerhost port=5432 dbname=db'
);
SELECT pglogical.wait_for_subscription_sync_complete('subscription1');
In addition to the SQL-level node and subscription creation, pglogical also
supports creating a subscriber by cloning the provider with pg_basebackup and
starting it up as a pglogical subscriber. This is done with the
pglogical_create_subscriber tool; see the --help output.
Unlike pglogical.create_subscription's data sync options, this clone ignores
replication sets and copies all tables on all databases. However, it's often
much faster, especially over high-bandwidth links.
Nodes can be added and removed dynamically using the SQL interfaces.
pglogical.create_node(node_name name, dsn text)
Creates a node.
Parameters:
node_name - name of the new node, only one node is allowed per databasedsn - connection string to the node, for nodes that are supposed to be
providers, this should be reachable from outsidepglogical.drop_node(node_name name, ifexists bool)
Drops the pglogical node.
Parameters:
node_name - name of an existing nodeifexists - if true, error is not thrown when subscription does not exist,
default is falsepglogical.alter_node_add_interface(node_name name, interface_name name, dsn text)
Adds additional interface to a node.
When node is created, the interface for it is also created with the dsn
specified in the create_node and with the same name as the node. This
interface allows adding alternative interfaces with different connection
strings to an existing node.
Parameters:
node_name - name of an existing nodeinterface_name - name of a new interface to be addeddsn - connection string to the node used for the new interfacepglogical.alter_node_drop_interface(node_name name, interface_name name)
Remove existing interface from a node.
Parameters:
node_name - name of and existing nodeinterface_name - name of an existing interfacepglogical.create_subscription(subscription_name name, provider_dsn text, replication_sets text[], synchronize_structure boolean, synchronize_data boolean, forward_origins text[], apply_delay interval)
Creates a subscription from current node to the provider node. Command does
not block, just initiates the action.
Parameters:
subscription_name - name of the subscription, must be uniqueprovider_dsn - connection string to a providerreplication_sets - array of replication sets to subscribe to, these must
already exist, default is "{default,default_insert_only,ddl_sql}"synchronize_structure - specifies if to synchronize structure from
provider to the subscriber, default falsesynchronize_data - specifies if to synchronize data from provider to
the subscriber, default trueforward_origins - array of origin names to forward, currently only
supported values are empty array meaning don't forward any changes
that didn't originate on provider node (this is useful for two-way
replication between the nodes), or "{all}" which means replicate all
changes no matter what is their origin, default is "{all}"apply_delay - how much to delay replication, default is 0 secondsforce_text_transfer - force the provider to replicate all columns
using a text representation (which is slower, but may be used to
change the type of a replicated column on the subscriber), default
is falseThe subscription_name is used as application_name by the replication
connection. This means that it's visible in the pg_stat_replication
monitoring view. It can also be used in synchronous_standby_names when
pglogical is used as part of
synchronous replication setup.
Use pglogical.wait_for_subscription_sync_complete(sub_name) to wait for the
subscription to asynchronously start replicating and complete any needed
schema and/or data sync.
pglogical.drop_subscription(subscription_name name, ifexists bool)
Disconnects the subscription and removes it from the catalog.
Parameters:
subscription_name - name of the existing subscriptionifexists - if true, error is not thrown when subscription does not exist,
default is falsepglogical.alter_subscription_disable(subscription_name name, immediate bool)
Disables a subscription and disconnects it from the provider.
Parameters:
subscription_name - name of the existing subscriptionimmediate - if true, the subscription is stopped immediately, otherwise
it will be only stopped at the end of current transaction, default is falsepglogical.alter_subscription_enable(subscription_name name, immediate bool)
Enables disabled subscription.
Parameters:
subscription_name - name of the existing subscriptionimmediate - if true, the subscription is started immediately, otherwise
it will be only started at the end of current transaction, default is falsepglogical.alter_subscription_interface(subscription_name name, interface_name name)
Switch the subscription to use different interface to connect to provider
node.
Parameters:
subscription_name - name of an existing subscriptioninterface_name - name of an existing interface of the current provider
nodepglogical.alter_subscription_synchronize(subscription_name name, truncate bool)
All unsynchronized tables in all sets are synchronized in a single operation.
Tables are copied and synchronized one by one. Command does not block, just
initiates the action. Use pglogical.wait_for_subscription_sync_complete
to wait for completion.
Parameters:
subscription_name - name of the existing subscriptiontruncate - if true, tables will be truncated before copy, default falsepglogical.alter_subscription_resynchronize_table(subscription_name name, relation regclass)
Resynchronize one existing table. The table may not be the target of any
foreign key constraints.
WARNING: This function will truncate the table immediately, and only then
begin synchronising it, so it will be empty while being synced
Does not block, use pglogical.wait_for_table_sync_complete to wait for
completion.
Parameters:
subscription_name - name of the existing subscriptionrelation - name of existing table, optionally qualifiedpglogical.wait_for_subscription_sync_complete(subscription_name name)
Wait for a subscription or to finish synchronization after a
pglogical.create_subscription or pglogical.alter_subscription_synchronize.
This function waits until the subscription's initial schema/data sync, if any, are done, and until any tables pending individual resynchronisation have also finished synchronising.
For best results, run SELECT pglogical.wait_slot_confirm_lsn(NULL, NULL) on the
provider after any replication set changes that requested resyncs, and only
then call pglogical.wait_for_subscription_sync_complete on the subscriber.
pglogical.wait_for_table_sync_complete(subscription_name name, relation regclass)
Same as pglogical.wait_for_subscription_sync_complete, but waits only for
the subscription's initial sync and the named table. Other tables pending
resynchronisation are ignored.
pglogical.wait_slot_confirm_lsn
SELECT pglogical.wait_slot_confirm_lsn(NULL, NULL)
Wait until all replication slots on the current node have replayed up to the
xlog insert position at time of call on all providers. Returns when
all slots' confirmed_flush_lsn passes the pg_current_wal_insert_lsn() at
time of call.
Optionally may wait for only one replication slot (first argument). Optionally may wait for an arbitrary LSN passed instead of the insert lsn (second argument). Both are usually just left null.
This function is very useful to ensure all subscribers have received changes up to a certain point on the provider.
pglogical.show_subscription_status(subscription_name name)
Shows status and basic information about subscription.
Parameters:
subscription_name - optional name of the existing subscription, when no
name was provided, the function will show status for all subscriptions on
local nodepglogical.show_subscription_table(subscription_name name, relation regclass)
Shows synchronization status of a table.
Parameters:
subscription_name - name of the existing subscriptionrelation - name of existing table, optionally qualifiedpglogical.alter_subscription_add_replication_set(subscription_name name, replication_set name)
Adds one replication set into a subscriber. Does not synchronize, only
activates consumption of events.
Parameters:
subscription_name - name of the existing subscriptionreplication_set - name of replication set to addpglogical.alter_subscription_remove_replication_set(subscription_name name, replication_set name)
Removes one replication set from a subscriber.
Parameters:
subscription_name - name of the existing subscriptionreplication_set - name of replication set to removeThere is also a postgresql.conf parameter,
pglogical.extra_connection_options, that may be set to assign connection
options that apply to all connections made by pglogical. This can be a useful
place to set up custom keepalive options, etc.
pglogical defaults to enabling TCP keepalives to ensure that it notices
when the upstream server disappears unexpectedly. To disable them add
keepalives = 0 to pglogical.extra_connection_options.
Replication sets provide a mechanism to control which tables in the database will be replicated and which actions on those tables will be replicated.
Each replicated set can specify individually if INSERTs, UPDATEs,
DELETEs and TRUNCATEs on the set are replicated. Every table can be in
multiple replication sets and every subscriber can subscribe to multiple
replication sets as well. The resulting set of tables and actions replicated
is the union of the sets the table is in. The tables are not replicated until
they are added into a replication set.
There are three preexisting replication sets named "default",
"default_insert_only" and "ddl_sql". The "default" replication set is defined
to replicate all changes to tables in it. The "default_insert_only" only
replicates INSERTs and is meant for tables that don't have primary key (see
Limitations section for details).
The "ddl_sql" replication set is defined to replicate schema changes specified by
pglogical.replicate_ddl_command
The following functions are provided for managing the replication sets:
pglogical.create_replication_set(set_name name, replicate_insert bool, replicate_update bool, replicate_delete bool, replicate_truncate bool)
This function creates a new replication set.
Parameters:
set_name - name of the set, must be uniquereplicate_insert - specifies if INSERT is replicated, default truereplicate_update - specifies if UPDATE is replicated, default truereplicate_delete - specifies if DELETE is replicated, default truereplicate_truncate - specifies if TRUNCATE is replicated, default truepglogical.alter_replication_set(set_name name, replicate_inserts bool, replicate_updates bool, replicate_deletes bool, replicate_truncate bool)
This function changes the parameters of the existing replication set.
Parameters:
set_name - name of the existing replication setreplicate_insert - specifies if INSERT is replicated, default truereplicate_update - specifies if UPDATE is replicated, default truereplicate_delete - specifies if DELETE is replicated, default truereplicate_truncate - specifies if TRUNCATE is replicated, default truepglogical.drop_replication_set(set_name text)
Removes the replication set.
Parameters:
set_name - name of the existing replication setpglogical.replication_set_add_table(set_name name, relation regclass, synchronize_data boolean, columns text[], row_filter text)
Adds a table to replication set.
Parameters:
set_name - name of the existing replication setrelation - name or OID of the table to be added to the setsynchronize_data - if true, the table data is synchronized on all
subscribers which are subscribed to given replication set, default falsecolumns - list of columns to replicate. Normally when all columns
should be replicated, this will be set to NULL which is the
defaultrow_filter - row filtering expression, default NULL (no filtering),
see Row Filtering for more info.
WARNING: Use caution when synchronizing data with a valid row filter.
Using synchronize_data=true with a valid row_filter is like a one-time operation for a table.
Executing it again with modified row_filter won't synchronize data to subscriber. Subscribers
may need to call pglogical.alter_subscription_resynchronize_table() to fix it.pglogical.replication_set_add_all_tables(set_name name, schema_names text[], synchronize_data boolean)
Adds all tables in given schemas. Only existing tables are added, table that
will be created in future will not be added automatically. For how to ensure
that tables created in future are added to correct replication set, see
Automatic assignment of replication sets for new tables.
Parameters:
set_name - name of the existing replication setschema_names - array of names name of existing schemas from which tables
should be addedsynchronize_data - if true, the table data is synchronized on all
subscribers which are subscribed to given replication set, default falsepglogical.replication_set_remove_table(set_name name, relation regclass)
Remove a table from replication set.
Parameters:
set_name - name of the existing replication setrelation - name or OID of the table to be removed from the setpglogical.replication_set_add_sequence(set_name name, relation regclass, synchronize_data boolean)
Adds a sequence to a replication set.
Parameters:
set_name - name of the existing replication setrelation - name or OID of the sequence to be added to the setsynchronize_data - if true, the sequence value will be synchronized immediately, default falsepglogical.replication_set_add_all_sequences(set_name name, schema_names text[], synchronize_data boolean)
Adds all sequences from the given schemas. Only existing sequences are added, any sequences that
will be created in future will not be added automatically.
Parameters:
set_name - name of the existing replication setschema_names - array of names name of existing schemas from which tables
should be addedsynchronize_data - if true, the sequence value will be synchronized immediately, default falsepglogical.replication_set_remove_sequence(set_name name, relation regclass)
Remove a sequence from a replication set.
Parameters:
set_name - name of the existing replication setrelation - name or OID of the sequence to be removed from the setYou can view the information about which table is in which set by querying the
pglogical.tables view.
The event trigger facility can be used for describing rules which define replication sets for newly created tables.
Example:
CREATE OR REPLACE FUNCTION pglogical_assign_repset()
RETURNS event_trigger AS $$
DECLARE obj record;
BEGIN
FOR obj IN SELECT * FROM pg_event_trigger_ddl_commands()
LOOP
IF obj.object_type = 'table' THEN
IF obj.schema_name = 'config' THEN
PERFORM pglogical.replication_set_add_table('configuration', obj.objid);
ELSIF NOT obj.in_extension THEN
PERFORM pglogical.replication_set_add_table('default', obj.objid);
END IF;
END IF;
END LOOP;
END;
$$ LANGUAGE plpgsql;
CREATE EVENT TRIGGER pglogical_assign_repset_trg
ON ddl_command_end
WHEN TAG IN ('CREATE TABLE', 'CREATE TABLE AS')
EXECUTE PROCEDURE pglogical_assign_repset();
The above example will put all new tables created in schema config into
replication set configuration and all other new tables which are not created
by extensions will go to default replication set.
pglogical.replicate_ddl_command(command text, replication_sets text[])
Execute locally and then send the specified command to the replication queue
for execution on subscribers which are subscribed to one of the specified
replication_sets.
Parameters:
command - DDL query to executereplication_sets - array of replication sets which this command should be
associated with, default "{ddl_sql}"pglogical.synchronize_sequence(relation regclass)
Push sequence state to all subscribers. Unlike the subscription and table
synchronization function, this function should be run on provider. It forces
update of the tracked sequence state which will be consumed by all
subscribers (replication set filtering still applies) once they replicate the
transaction in which this function has been executed.
Parameters:
relation - name of existing sequence, optionally qualifiedPGLogical allows row based filtering both on provider side and the subscriber side.
On the provider the row filtering can be done by specifying row_filter
parameter for the pglogical.replication_set_add_table function. The
row_filter is normal PostgreSQL expression which has the same limitations
on what's allowed as the CHECK constraint.
Simple row_filter would look something like row_filter := 'id > 0' which
would ensure that only rows where values of id column is bigger than zero
will be replicated.
It's allowed to use volatile function inside row_filter but caution must
be exercised with regard to writes as any expression which will do writes
will throw error and stop replication.
It's also worth noting that the row_filter is running inside the replication
session so session specific expressions such as CURRENT_USER will have
values of the replication session and not the session which did the writes.
On the subscriber the row based filtering can be implemented using standard
BEFORE TRIGGER mechanism.
It is required to mark any such triggers as either ENABLE REPLICA or
ENABLE ALWAYS otherwise they will not be executed by the replication
process.
Synchronous replication is supported using same standard mechanism provided by PostgreSQL for physical replication.
The synchronous_commit and synchronous_standby_names settings will affect
when COMMIT command reports success to client if pglogical subscription
name is used in synchronous_standby_names. Refer to PostgreSQL
documentation for more info about how to configure these two variables.
In case the node is subscribed to multiple providers, or when local writes happen on a subscriber, conflicts can arise for the incoming changes. These are automatically detected and can be acted on depending on the configuration.
The configuration of the conflicts resolver is done via the
pglogical.conflict_resolution setting.
The resolved conflicts are logged using the log level set using
pglogical.conflict_log_level. This parameter defaults to LOG. If set to
lower level than log_min_messages the resolved conflicts won't appear in
the server log.
Some aspects of PGLogical can be configured using configuration options that
can be either set in postgresql.conf or via ALTER SYSTEM SET.
pglogical.conflict_resolution
Sets the resolution method for any detected conflicts between local data
and incoming changes.
Possible values:
error - the replication will stop on error if conflict is detected and
manual action is needed for resolvingapply_remote - always apply the change that's conflicting with local
datakeep_local - keep the local version of the data and ignore the
conflicting change that is coming from the remote nodelast_update_wins - the version of data with newest commit timestamp
will be kept (this can be either local or remote version)first_update_wins - the version of the data with oldest timestamp will
be kept (this can be either local or remote version)The available settings and defaults depend on version of PostgreSQL and other settings.
The default value in PostgreSQL is apply_remote.
The keep_local, last_update_wins and first_update_wins settings
require track_commit_timestamp PostgreSQL setting to be enabled. As
track_commit_timestamp is not available in PostgreSQL 9.4
pglogical.conflict_resolution can only be apply_remote or error.
In Postgres-XL, the only supported value and the default is error.
pglogical.conflict_log_level
Sets the log level for reporting detected conflicts when the
pglogical.conflict_re