I am running database Agens Graph v.2.1.0. I have created two graphs with the same structure such as 1 vertex label "VERTEX" and 1 edge label "EDGE". How can I copy data from one graph to another? I can`t copy data with sql query from ag_edge, ag_vertex tables. Is there any relevant example?
Maybe a function to create full copy of graph?
I have the procedure explained here and code in go language that does it. Go code can be easily rewritten in C or any scripting language. Here it is again:
AgensGraph is a new generation multi-model graph database for the modern complex data environment.
Sometimes it seems useful to be able to clone the whole graph into another graph in the same database. AgensGraph have not produced such a utility. Here is a try to create such a utility in Go language.
AgensGraph is an extension of PostgreSQL. So, in AgensGraph a graph is a schema (set of tables with data) and some metadata in tables pg_catalog.ag_label, pg_catalog.ag_graph and pg_catalog.ag_graphmeta. The data is a set of tables with indexes containing information about vertexes and edges connecting them.
It, obviously, means to create a new_schema that will be a copy of the original schema (lets call it old_schema for brevity) and to set up the metadata in the tables mentioned above properly.
Described in PostgreSQL: How to create full copy of database schema in same database?. Shortly:
psql -U user -d dbname -c 'ALTER SCHEMA old_schema RENAME TO new_schema'
pg_dump -U user -n new_schema -f new_schema.sql dbname
psql -U user -d dbname -c 'ALTER SCHEMA new_schema RENAME TO old_schema'
psql -U user -d dbname -c 'CREATE SCHEMA new_schema'
psql -U user -q -d dbname -f new_schema.sql
rm new_schema.sql
In order to do it successfully we need to remove the old_schema from ag_graph table before renaming old_schema and then adding it back before creating new schema - otherwise AgensGraph triggers will prohibit schema from renaming (see Go code).
agens=# \d ag_graph;
Table "pg_catalog.ag_graph"
Column | Type | Collation | Nullable | Default
-----------+------+-----------+----------+---------
graphname | name | | not null |
nspid | oid | | not null |
Indexes:
"ag_graph_graphname_index" UNIQUE, btree (graphname)
"ag_graph_oid_index" UNIQUE, btree (oid)
graphname == new_schema, nspid is taken from
agens=# SELECT oid FROM pg_namespace WHERE nspname='new_schema';
oid
-------
16418
(1 row)
16419 == (nspid+1) of old_schema
agens=# SELECT * FROM ag_label WHERE graphid=16419;
labname | graphid | labid | relid | labkind
-----------+---------+-------+-------+---------
ag_vertex | 16419 | 1 | 16424 | v
ag_edge | 16419 | 2 | 16438 | e
person | 16419 | 3 | 16453 | v
knows | 16419 | 4 | 16467 | e
(4 rows)
We need to copy all those records with the same labname, labid, labkind and new graphid == (nspid+1) of new_schema and relid == relfilenode from pg_class:
agens=# SELECT relname, relfilenode FROM pg_class WHERE relnamespace=16418;
relname | relfilenode
-------------------+-------------
ag_label_seq | 16420
knows | 16467
ag_vertex_pkey | 16433
ag_vertex_id_seq | 16435
ag_edge_id_idx | 16447
ag_edge_start_idx | 16448
ag_edge_end_idx | 16449
ag_edge_id_seq | 16450
ag_vertex | 16424
person | 16453
person_pkey | 16462
person_id_seq | 16464
ag_edge | 16438
knows_id_idx | 16476
knows_start_idx | 16477
knows_end_idx | 16478
knows_id_seq | 16479
(17 rows)
relnamespace is a nspid of new_schema, all the indexes and primary keys need to be ignored, only tables need to be copied.
I have no idea - it was always empty in my case.
All of above looks like a plan to me - so, I tried to implement that in a simple Go language utility: https://github.com/tbolsh/CloneAgensGraph
