DOKK / manpages / debian 12 / pgcopydb / pgcopydb snapshot.1.en
PGCOPYDB SNAPSHOT(1) pgcopydb PGCOPYDB SNAPSHOT(1)

pgcopydb snapshot - pgcopydb snapshot

pgcopydb snapshot - Create and exports a snapshot on the source database

The command pgcopydb snapshot connects to the source database and executes a SQL query to export a snapshot. The obtained snapshot is both printed on stdout and also in a file where other pgcopydb commands might expect to find it.

pgcopydb snapshot: Create and exports a snapshot on the source database
usage: pgcopydb snapshot  --source ...


  --source         Postgres URI to the source database


  --dir            Work directory to use


The following options are available to pgcopydb create and pgcopydb drop subcommands:

Connection string to the source Postgres instance. See the Postgres documentation for connection strings for the details. In short both the quoted form "host=... dbname=..." and the URI form postgres://user@host:5432/dbname are supported.
During its normal operations pgcopydb creates a lot of temporary files to track sub-processes progress. Temporary files are created in the directory location given by this option, or defaults to ${TMPDIR}/pgcopydb when the environment variable is set, or then to /tmp/pgcopydb.
Instead of exporting its own snapshot by calling the PostgreSQL function pg_export_snapshot() it is possible for pgcopydb to re-use an already exported snapshot.
Logical replication slot name to use, default to pgcopydb. The slot should be created within the same transaction snapshot as the initial data copy.

Must be using the wal2json output plugin, available with format-version 2.

Logical replication target system needs to track the transactions that have been applied already, so that in case we get disconnected or need to resume operations we can skip already replayed transaction.

Postgres uses a notion of an origin node name as documented in Replication Progress Tracking. This option allows to pick your own node name and defaults to "pgcopydb". Picking a different name is useful in some advanced scenarios like migrating several sources in the same target, where each source should have their own unique origin node name.

Logical replication target system registers progress by assigning a current LSN to the --origin node name. When creating an origin on the target database system, it is required to provide the current LSN from the source database system, in order to properly bootstrap pgcopydb logical decoding.
Increase current verbosity. The default level of verbosity is INFO. In ascending order pgcopydb knows about the following verbosity levels: FATAL, ERROR, WARN, INFO, NOTICE, DEBUG, TRACE.
Set current verbosity to DEBUG level.
Set current verbosity to TRACE level.
Set current verbosity to ERROR level.

PGCOPYDB_SOURCE_PGURI

Connection string to the source Postgres instance. When --source is ommitted from the command line, then this environment variable is used.


Create a snapshot on the source database in the background:

$ pgcopydb snapshot &
[1] 72938
17:31:52 72938 INFO  Running pgcopydb version 0.7.13.gcbf2d16.dirty from "/Users/dim/dev/PostgreSQL/pgcopydb/./src/bin/pgcopydb/pgcopydb"
17:31:52 72938 INFO  Using work dir "/var/folders/d7/zzxmgs9s16gdxxcm0hs0sssw0000gn/T//pgcopydb"
17:31:52 72938 INFO  Removing the stale pid file "/var/folders/d7/zzxmgs9s16gdxxcm0hs0sssw0000gn/T//pgcopydb/pgcopydb.aux.pid"
17:31:52 72938 INFO  Work directory "/var/folders/d7/zzxmgs9s16gdxxcm0hs0sssw0000gn/T//pgcopydb" already exists
17:31:52 72938 INFO  Exported snapshot "00000003-000CB5FE-1" from the source database
00000003-000CB5FE-1


And when the process is done, stop maintaining the snapshot in the background:

$ kill %1
17:31:56 72938 INFO  Asked to terminate, aborting
[1]+  Done                    pgcopydb snapshot


Dimitri Fontaine

2022, Dimitri Fontaine

November 3, 2022 0.10