As ltcluster uses pg_basebackup
to clone a standby, it's possible to
provide additional parameters for pg_basebackup
to customise the
cloning process.
By default, pg_basebackup
performs a checkpoint before beginning the backup
process. However, a normal checkpoint may take some time to complete;
a fast checkpoint can be forced with ltcluster standby clone
's
-c/--fast-checkpoint
option.
Note that this may impact performance of the server being cloned from (typically the primary)
so should be used with care.
Other options can be passed to pg_basebackup
by including them
in the ltcluster.conf
setting pg_basebackup_options
.
Not that by default, ltcluster executes pg_basebackup
with -X/--wal-method
set to stream
.
From LightDB 21, if replication slots are in use, it will also create a replication slot before
running the base backup, and execute pg_basebackup
with the
-S/--slot
option set to the name of the previously created replication slot.
These parameters can set by the user in pg_basebackup_options
, in which case they
will override the ltcluster default values. However normally there's no reason to do this.
If using a separate directory to store WAL files, provide the option --waldir
with the absolute path to the
WAL directory. Any WALs generated during the cloning process will be copied here, and
a symlink will automatically be created from the main data directory.
See the LightDB pg_basebackup documentation for more details of available options.
If replication connections to a standby's upstream server are password-protected, the standby must be able to provide the password so it can begin streaming replication.
The recommended way to do this is to store the password in the lightdb
system
user's ~/.pgpass
file. For more information on using the password file, see
the documentation section password file.
If using a pgpass
file, an entry for the replication user (by default the
user who connects to the ltcluster
database) must
be provided, with database name set to replication
, e.g.:
node1:5432:replication:ltcluster:12345
If, for whatever reason, you wish to include the password in recovery.conf
,
set use_primary_conninfo_password
to true
in
ltcluster.conf
. This will read a password set in PGPASSWORD
(but not ~/.pgpass
) and place it into the primary_conninfo
string in recovery.conf
. Note that PGPASSWORD
will need to be set during any action which causes recovery.conf
to be
rewritten, e.g. ltcluster standby follow.
In some circumstances it might be desirable to create a dedicated replication-only
user (in addition to the user who manages the ltcluster metadata). In this case,
the replication user should be set in ltcluster.conf
via the parameter
replication_user
; ltcluster will use this value when making
replication connections and generating recovery.conf
. This
value will also be stored in the parameter ltcluster.nodes
table for each node; it no longer needs to be explicitly specified when
cloning a node or executing ltcluster standby follow.
ltcluster provides a tablespace_mapping
configuration
file option, which will makes it possible to map the tablespace on the source node to
a different location on the local node.
To use this, add tablespace_mapping
to ltcluster.conf
like this:
tablespace_mapping='/var/lib/pgsql/tblspc1=/data/pgsql/tblspc1'
where the left-hand value represents the tablespace on the source node, and the right-hand value represents the tablespace on the standby to be cloned.
This parameter can be provided multiple times.