Man page - pgcopydb snapshot(1)

Manual

PGCOPYDB SNAPSHOT

NAME
OPTIONS
ENVIRONMENT
EXAMPLES
AUTHOR
COPYRIGHT

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NAME

pgcopydb snapshot - 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 form postgres://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 specified by this option, or defaults to ${TMPDIR}/pgcopydb when the environment variable is set, or otherwise 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

AUTHOR

Dimitri Fontaine

COPYRIGHT

2022-2024, Dimitri Fontaine

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