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repmgrd: refactor standby monitoring status query and code

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This had grown somewhat complex with addition of handling for
various corner cases. Much of the work has now been delegated
to the query itself.
This commit is contained in:
Ian Barwick
2016-08-16 15:19:06 +09:00
parent 6bd1c6a36d
commit ef7bed1b3d
1 changed files with 20 additions and 51 deletions
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71
repmgrd.c
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@@ -718,13 +718,14 @@ static void
standby_monitor(void)
{
PGresult *res;
char sqlquery[QUERY_STR_LEN];
char monitor_standby_timestamp[MAXLEN];
char last_wal_primary_location[MAXLEN];
char last_xlog_receive_location[MAXLEN];
char last_xlog_replay_location[MAXLEN];
char last_xact_replay_timestamp[MAXLEN];
bool last_xlog_receive_location_gte_replayed;
char sqlquery[QUERY_STR_LEN];
bool receiving_streamed_wal = true;
XLogRecPtr lsn_master_current_xlog_location;
XLogRecPtr lsn_last_xlog_receive_location;
@@ -745,7 +746,6 @@ standby_monitor(void)
int active_master_id;
const char *upstream_node_type = NULL;
bool receiving_streamed_wal = true;
/*
@@ -1080,14 +1080,21 @@ standby_monitor(void)
if (wait_connection_availability(master_conn, local_options.master_response_timeout) != 1)
return;
/* Get local xlog info */
/* Get local xlog info
*
* If receive_location is NULL, we're in archive recovery and not streaming WAL
* If receive_location is less than replay location, we were streaming WAL but are
* somehow disconnected and evidently in archive recovery
*/
sqlquery_snprintf(sqlquery,
" SELECT ts, "
" receive_location, "
" CASE WHEN (receive_location IS NULL OR receive_location < replay_location) "
" THEN replay_location "
" ELSE receive_location"
" END AS receive_location,"
" replay_location, "
" replay_timestamp, "
" receive_location >= replay_location "
" COALESCE(receive_location, '0/0') >= replay_location AS receiving_streamed_wal "
" FROM (SELECT CURRENT_TIMESTAMP AS ts, "
" pg_catalog.pg_last_xlog_receive_location() AS receive_location, "
" pg_catalog.pg_last_xlog_replay_location() AS replay_location, "
@@ -1095,6 +1102,7 @@ standby_monitor(void)
" ) q ");
res = PQexec(my_local_conn, sqlquery);
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
@@ -1109,40 +1117,17 @@ standby_monitor(void)
strncpy(last_xlog_replay_location, PQgetvalue(res, 0, 2), MAXLEN);
strncpy(last_xact_replay_timestamp, PQgetvalue(res, 0, 3), MAXLEN);
last_xlog_receive_location_gte_replayed = (strcmp(PQgetvalue(res, 0, 4), "t") == 0)
receiving_streamed_wal = (strcmp(PQgetvalue(res, 0, 4), "t") == 0)
? true
: false;
/*
* If pg_last_xlog_receive_location is NULL, this means we're in archive
* recovery and will need to calculate lag based on pg_last_xlog_replay_location
*/
/*
* Replayed WAL is greater than received streamed WAL
*/
if (PQgetisnull(res, 0, 1))
if (receiving_streamed_wal == false)
{
receiving_streamed_wal = false;
log_verbose(LOG_DEBUG, _("standby %i not connected to streaming replication"), local_options.node);
}
PQclear(res);
/*
* In the unusual event of a standby becoming disconnected from the primary,
* while this repmgrd remains connected to the primary, subtracting
* "last_xlog_replay_location" from "lsn_last_xlog_receive_location" and coercing to
* (long long unsigned int) will result in a meaningless, very large
* value which will overflow a BIGINT column and spew error messages into the
* PostgreSQL log. In the absence of a better strategy, skip attempting
* to insert a monitoring record.
*/
if (receiving_streamed_wal == true && last_xlog_receive_location_gte_replayed == false)
{
log_verbose(LOG_WARNING,
"Replayed WAL newer than received WAL - is this standby connected to its upstream?\n");
}
/*
* Get master xlog position
*
@@ -1164,25 +1149,9 @@ standby_monitor(void)
lsn_master_current_xlog_location = lsn_to_xlogrecptr(last_wal_primary_location, NULL);
lsn_last_xlog_replay_location = lsn_to_xlogrecptr(last_xlog_replay_location, NULL);
lsn_last_xlog_receive_location = lsn_to_xlogrecptr(last_xlog_receive_location, NULL);
/* Calculate apply lag */
if (last_xlog_receive_location_gte_replayed == false)
{
/*
* We're not receiving streaming WAL - in this case the receive location
* equals the last replayed location
*/
apply_lag = 0;
strncpy(last_xlog_receive_location, last_xlog_replay_location, MAXLEN);
lsn_last_xlog_receive_location = lsn_to_xlogrecptr(last_xlog_replay_location, NULL);
}
else
{
lsn_last_xlog_receive_location = lsn_to_xlogrecptr(last_xlog_receive_location, NULL);
apply_lag = (long long unsigned int)lsn_last_xlog_receive_location - lsn_last_xlog_replay_location;
}
apply_lag = (long long unsigned int)lsn_last_xlog_receive_location - lsn_last_xlog_replay_location;
/* Calculate replication lag */
if (lsn_master_current_xlog_location >= lsn_last_xlog_receive_location)