本頁說明如何使用 PostgreSQL 可觀測性指令碼，監控 AlloyDB Omni 資料庫效能。
查看已連線程序的狀態和等待事件
您可以查詢 pg_stat_activity 檢視畫面，判斷與 AlloyDB Omni 執行個體連線的任何程序，以及等待活動的任何後端。
SELECT
pid,
datname,
age(backend_xid) AS age_in_xids,
now() - xact_start AS xact_age,
now() - query_start AS query_age,
state,
wait_event_type,
wait_event,
query_id,
query
FROM
pg_stat_activity
WHERE
state != 'idle'
AND pid <> pg_backend_pid()
ORDER BY
4 DESC
LIMIT 10;
查看最大的資料表
您可以查詢 pg_stat_user_tables 檢視畫面，判斷最大資料表的大小。
SELECT
oid,
oid::regclass table_name,
pg_size_pretty(pg_relation_size(oid)),
relpages,
s.seq_scan,
s.idx_scan
FROM
pg_class,
pg_stat_user_tables s
WHERE
s.relid = oid
AND oid > 16383
AND relpages > 100
AND relkind = 'r'
ORDER BY
relpages DESC
LIMIT 20;
查看最常連續掃描的項目
您可以查詢 pg_stat_user_tables 檢視畫面，查看熱門連續掃描。
SELECT
relid,
relname,
seq_scan,
pg_size_pretty(pg_relation_size(relid))
FROM
pg_stat_user_tables
ORDER BY
seq_scan DESC
LIMIT 15;
查看索引掃描作業
您可以查詢 pg_stat_user_tables 檢視畫面，查看索引掃描次數最多的項目。
SELECT
relid,
relid::regclass table_name,
idx_scan,
pg_size_pretty(pg_relation_size(relid))
FROM
pg_stat_user_tables
WHERE
idx_scan > 10
ORDER BY
idx_scan DESC
LIMIT 15;
查看執行時間最長的交易
您可以查詢 pg_stat_activity 檢視畫面，並檢查交易的存續時間，藉此查看執行時間最長的交易。
SELECT
pid,
age(backend_xid) AS age_in_xids,
now() - xact_start AS xact_age,
now() - query_start AS query_age,
state,
query
FROM
pg_stat_activity
WHERE
state != 'idle'
ORDER BY
2 DESC
LIMIT 10;
查看吸塵進度
您可以查詢 pg_stat_progress_vacuum 檢視區塊，並使用程序 ID 將其與 pg_stat_activity 檢視區塊聯結，藉此查看清除作業的進度。
SELECT
p.pid,
now() - a.xact_start AS duration,
coalesce(wait_event_type ||'.'|| wait_event, 'f') AS waiting,
CASE
WHEN a.query ~*'^autovacuum.*to prevent wraparound' THEN 'wraparound'
WHEN a.query ~*'^vacuum' THEN 'user'
ELSE
'regular'
END AS mode,
p.datname AS database,
p.relid::regclass AS table,
p.phase,
pg_size_pretty(p.heap_blks_total * current_setting('block_size')::int) AS table_size,
pg_size_pretty(pg_total_relation_size(relid)) AS total_size,
pg_size_pretty(p.heap_blks_scanned * current_setting('block_size')::int) AS scanned,
pg_size_pretty(p.heap_blks_vacuumed * current_setting('block_size')::int) AS vacuumed,
round(100.0 * p.heap_blks_scanned / p.heap_blks_total, 1) AS scanned_pct,
round(100.0 * p.heap_blks_vacuumed / p.heap_blks_total, 1) AS vacuumed_pct,
p.index_vacuum_count,
round(100.0 * p.num_dead_tuples / p.max_dead_tuples,1) AS dead_pct
FROM pg_stat_progress_vacuum p
JOIN pg_stat_activity a using (pid)
ORDER BY now() - a.xact_start DESC;
查看非同步查詢
如要查看非同步執行的查詢，可以查詢 pg_stat_activity 檢視畫面，並篩選出非領導程序的查詢。
SELECT
query,
leader_pid,
array_agg(pid) FILTER (WHERE leader_pid != pid) AS members
FROM
pg_stat_activity
WHERE
leader_pid IS NOT NULL
GROUP BY
query,
leader_pid;
查看封鎖鎖定 SQL
您可以查詢 pg_locks 檢視畫面，並與 pg_stat_activity 檢視畫面聯結，查看遭封鎖的活動。
SELECT blocked_locks.pid AS blocked_pid,
blocked_activity.usename AS blocked_user,
blocking_locks.pid AS blocking_pid,
blocking_activity.usename AS blocking_user,
blocked_activity.query AS blocked_statement,
blocked_activity.wait_event AS blocked_wait_event,
blocking_activity.wait_event AS blocking_wait_event,
blocking_activity.query AS current_statement_in_blocking_process
FROM pg_catalog.pg_locks blocked_locks
JOIN pg_catalog.pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid
JOIN pg_catalog.pg_locks blocking_locks
ON blocking_locks.locktype = blocked_locks.locktype
AND blocking_locks.database IS NOT DISTINCT FROM blocked_locks.database
AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
AND blocking_locks.pid != blocked_locks.pid
JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
WHERE NOT blocked_locks.granted;
判斷 work_mem 和 temp_buffers 大小的有效性
如要判斷 work_mem 和 temp_buffers 的大小是否符合需求，可以查詢 pg_stat_database 檢視畫面並檢查 postgres.log 檔案。
使用 pg_stat_database 執行下列查詢，如果執行之間 temp_files 或 temp_bytes 有任何成長，則可能需要調整 work_mem 或 temp_buffers。
SELECT
datname,
temp_files,
temp_bytes
FROM
pg_stat_database;
執行這項操作後，請檢查 postgres.log 檔案，看看是否使用了暫存檔案：
LOG: [fd.c:1772] temporary file: path "base/pgsql_tmp/pgsql_tmp4640.1", size 139264
目標是盡量減少建立暫時檔案，而不是完全避免建立。這是因為同時設定 work_mem 和 temp_buffers 時，必須在主機上的可用記憶體和需要記憶體的連線數量之間取得平衡。如要正確設定這些參數，您必須瞭解各個工作負載。