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
  --follow         Implement logical decoding to replay changes
  --plugin         Output plugin to use (test_decoding, wal2json)
  --slot-name      Use this Postgres replication slot name


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.


When the --follow option is used then pgcopydb implements Change Data Capture as detailed in the manual page for pgcopydb follow in parallel to the main copy database steps.

The replication slot is created using the Postgres replication protocol command CREATE_REPLICATION_SLOT, which then exports the snapshot being used in that command.


Logical decoding output plugin to use. The default is test_decoding which ships with Postgres core itself, so is probably already available on your source server.

It is possible to use wal2json instead. The support for wal2json is mostly historical in pgcopydb, it should not make a user visible difference whether you use the default test_decoding or wal2json.


Logical decoding slot name to use.


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.



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/"
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

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