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Using the last replayed LSN as the value of LSN location if the last received LSN is at the starting point of the WAL segment #227

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Using the last replayed LSN as the value of LSN location if the last received LSN is at the starting point of the WAL segment #227

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Using the last replayed LSN as the value of LSN location if the last …
gavinThinking Apr 7, 2024
686a375
Update pgsqlms
gavinThinking Apr 8, 2024
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53 changes: 53 additions & 0 deletions script/pgsqlms
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Original file line number Diff line number Diff line change
Expand Up @@ -207,6 +207,41 @@ sub _get_last_received_lsn {
return undef;
}

# Get the last write-ahead log location that has been replayed during recovery on a standby
# if the first argument is true, returns the value as decimal
# if the first argument is false, returns the value as LSN
# Returns undef if query failed
sub _get_last_replay_lsn {
my ( $dec ) = @_;
my $pg_last_wal_replay_lsn = 'pg_last_wal_replay_lsn()';
my $pg_wal_lsn_diff = 'pg_wal_lsn_diff';
my $query;
my $rc;
my @rs;

if ( $PGVERNUM < $PGVER_10 ) {
$pg_last_wal_receive_lsn = 'pg_last_xlog_replay_location()';
$pg_wal_lsn_diff = 'pg_xlog_location_diff';
}

if ( $dec ) {
$query = "SELECT $pg_wal_lsn_diff( $pg_last_wal_replay_lsn, '0/0' )";
}
else {
$query = "SELECT $pg_last_wal_replay_lsn";
}

$rc = _query( $query, \@rs );

return $rs[0][0] if $rc == 0 and $rs[0][0];

ocf_log( 'err', 'Could not query last replayed LSN (%s)', $rc ) if $rc != 0;
ocf_log( 'err', 'No values for last replayed LSN' )
if $rc == 0 and not $rs[0][0];

return undef;
}

# Get the master score for each connected standby
# Returns directly the result set of the query or exit with an error.
# Exits with OCF_ERR_GENERIC if the query failed
Expand Down Expand Up @@ -2060,6 +2095,24 @@ sub pgsql_notify_pre_promote {
_query( q{ CHECKPOINT }, {} );
%cdata = _get_controldata();
$node_lsn = _get_last_received_lsn( 'in decimal' );
# Checking if the current LSN are accurate
# In most cases, the pg_last_wal_receive_lsn() can accurately retrieve the last received LSN location
# When Postgres is started as a standby, the value obtained by this function is the starting point of the last
# WAL segment in the local pg_wal folder.
# After executing stream replication from primary, this value will be correctly updated.
my $WAL_SEGMENT_START = '000000';
# Convert LSN to hexadecimal
my $node_lsn_hexadecimal = sprintf("%X", $node_lsn);
# If the last three bytes (or six hexadecimal digits) of the LSN are zeros,
# It means that the LSN is the starting point of the last WAL segment in the local pg_wal folder.
if ($node_lsn_hexadecimal =~ /$WAL_SEGMENT_START$/) {
ocf_log( 'info', 'the LSN "%s" is not accurate', $node_lsn_hexadecimal);
my $node_last_replayed_lsn = _get_last_replay_lsn( 'in decimal' );
if ($node_last_replayed_lsn > $node_lsn) {
ocf_log( 'info', 'Using the last replayed LSN "%s" as the value for LSN location.', $node_last_replayed_lsn);
$node_lsn = $node_last_replayed_lsn;
}
}

unless ( defined $node_lsn ) {
ocf_log( 'warning', 'Unknown current node LSN' );
Expand Down