pgcopydb snapshot
pgcopydb snapshot - Create and export 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 export 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)
--wal2json-numeric-as-string Print numeric data type as string when using wal2json output plugin
--slot-name Use this Postgres replication slot name
Options
The following options are available to pgcopydb snapshot
:
- --source
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 formpostgres://user@host:5432/dbname
are supported.- --dir
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
.- --follow
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.
- --plugin
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.
- --wal2json-numeric-as-string
When using the wal2json output plugin, it is possible to use the
--wal2json-numeric-as-string
option to instruct wal2json to output numeric values as strings and thus prevent some precision loss.You need to have a wal2json plugin version on source database that supports
--numeric-data-types-as-string
option to use this option.See also the documentation for wal2json regarding this option for details.
- --slot-name
Logical decoding slot name to use.
- --verbose
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.
- --debug
Set current verbosity to DEBUG level.
- --trace
Set current verbosity to TRACE level.
- --quiet
Set current verbosity to ERROR level.
Environment
PGCOPYDB_SOURCE_PGURI
Connection string to the source Postgres instance. When
--source
is ommitted from the command line, then this environment variable is used.
PGCOPYDB_OUTPUT_PLUGIN
Logical decoding output plugin to use. When
--plugin
is omitted from the command line, then this environment variable is used.
PGCOPYDB_WAL2JSON_NUMERIC_AS_STRING
When true (or yes, or on, or 1, same input as a Postgres boolean) then pgcopydb uses the wal2json option
--numeric-data-types-as-string
when using the wal2json output plugin.When
--wal2json-numeric-as-string
is ommitted from the command line then this environment variable is used.
Examples
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