lolor

lolor is an extension that makes Postgres' Large Objects compatible with Logical Replication.

Table of Contents

• lolor Overview
• Building and Installing lolor
• Basic Configuration
• Using lolor
• Limitations
• Using pg_upgrade with lolor
• Release Notes

PostgreSQL supports large objects as related chunks as described in the pg_largeobject table. Large objects provide stream-style access to user data stored in a special large-object structure in the catalog. Large objects stored in catalog tables require special handling during replication; the lolor extension allows for the storage of large objects in non-catalog tables, aiding in replication of large objects.

lolor creates and manages large object related tables in the lolor schema:

lolor.pg_largeobject
lolor.pg_largeobject_metadata

PostgreSQL large objects allow you to store huge files within the database. Each large object is recognised by an OID that is assigned at the time of its creation. lolor stores objects in smaller segments within a separate system table and generates associated OIDs for large objects that are distinct from those of native large objects.

Use of the lolor extension requires Postgres 16 or newer.

Building and Installing lolor

You can also compile and install the extension from the source code, with the same guidelines as any other Postgres extension constructed using PGXS. Make sure that your PATH environment variable includes the directory where pg_config (under your Postgres installation) is located.

export PATH=/usr/pgsql-17/bin:$PATH

# compile
make USE_PGXS=1
# install, might be requiring sudo for the installation step
make USE_PGXS=1 install

After installing the lolor extension, connect to your Postgres database and create the extension with the command:

CREATE EXTENSION lolor;

Configuring lolor

You must set the lolor.node parameter before using the extension. The value can be from 1 to 2^28; the value is used to help in generation of new large object OID.

lolor.node = 1

You can also change the search_path to pick large object related tables from the lolor schema:

set search_path=lolor,"$user",public,pg_catalog

Any existing methods in pg_catalog.lo_* are renamed to pg_catalog.lo_*_orig, and new versions of these methods are introduced. If you remove the extension, the renamed pg_catalog.lo_*_orig functions are restored to their initial names.

While using pgedge replication with large objects, you must have the tables pg_largeobject and pg_largeobject_metadata in your replication set; use the following commands to add the tables:

./pgedge spock repset-add-table spock_replication_set 'lolor.pg_largeobject' lolor_db
./pgedge spock repset-add-table spock_replication_set 'lolor.pg_largeobject_metadata' lolor_db

Migrating large objects

Migration from native to lolor is manual; migration back is automatic on DROP EXTENSION so no objects are ever lost.

Migrate existing native large objects into lolor storage (requires superuser):

CREATE EXTENSION lolor;
SELECT lolor.migrate_from_native();

Reverse migration happens automatically when the extension is dropped, or can be triggered manually:

SELECT lolor.migrate_to_native();  -- manual
DROP EXTENSION lolor;              -- automatic

Both directions preserve original OIDs, owners, ACLs, and data.

Limitations

• Native large object functionality cannot be used while you are using the lolor extension.
• lolor does not support the following statements: ALTER LARGE OBJECT, GRANT ON LARGE OBJECT, COMMENT ON LARGE OBJECT, and REVOKE ON LARGE OBJECT.
• Large object migration must be performed from a single writer. Run migrate_from_native() on one node and let the migrated rows replicate to the other nodes (or add nodes afterward); the migrated objects and any newly created large objects are then collision-free, since new OIDs are node-encoded via lolor.node and generated OIDs are checked against existing rows. Running migrate_from_native() independently on more than one already-active node is not supported, because migrated objects preserve their original native OIDs, which lack node-encoding and can collide across nodes.