What is a PostgreSQL checkpoint?
A checkpoint is a point in the transaction log sequence at which all data files have been updated to reflect the information in the log. All data files will be flushed to disk. Refer to Section 29.4 for more details about what happens during a checkpoint.
What are Wal files?
The write-ahead log or “wal” file is a roll-forward journal that records transactions that have been committed but not yet applied to the main database. Details on the format of the wal file are describe in the WAL format subsection of the main file format document.
Why does PG _ basebackup not switch to a new Wal file?
The backup history file is not created in the database cluster backed up. pg_basebackup cannot force the standby to switch to a new WAL file at the end of backup. When you are using -X none, if write activity on the primary is low, pg_basebackup may need to wait a long time for the last WAL file required for the backup to be switched and archived.
Where to write the output of PG base backup?
Directory to write the output to. pg_basebackup will create the directory and any parent directories if necessary. The directory may already exist, but it is an error if the directory already exists and is not empty. When the backup is in tar mode, and the directory is specified as – (dash), the tar file will be written to stdout.
How many WAL segments are in PG _ xlog Directory?
The number of WAL segment files in pg_xlog directory depends on min_wal_size, max_wal_size and the amount of WAL generated in previous checkpoint cycles. When old log segment files are no longer needed, they are removed or recycled (that is, renamed to become future segments in the numbered sequence).
When to run PG _ switch _ Wal on the primary?
When you are using -X none, if write activity on the primary is low, pg_basebackup may need to wait a long time for the last WAL file required for the backup to be switched and archived. In this case, it may be useful to run pg_switch_wal on the primary in order to trigger an immediate WAL file switch.