本页介绍了如何使用 PostgreSQL 可观测性脚本监控 AlloyDB Omni 数据库性能。
查看关联的进程和等待事件的状态
您可以通过查询 pg_stat_activity 视图来确定连接到 AlloyDB Omni 实例的进程的状态，以及正在等待活动的任何后端。
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;
查看最大的表
您可以通过查询 pg_stat_user_tables 视图来确定最大的表的大小。
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;
查看顺序扫描次数最多的应用
您可以通过查询 pg_stat_user_tables 视图来查看热门顺序扫描。
SELECT
relid,
relname,
seq_scan,
pg_size_pretty(pg_relation_size(relid))
FROM
pg_stat_user_tables
ORDER BY
seq_scan DESC
LIMIT 15;
查看索引扫描次数最多的索引
您可以通过查询 pg_stat_user_tables 视图来查看热门索引扫描。
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;
查看运行时间最长的事务
您可以通过查询 pg_stat_activity 视图并检查每个事务的存在时间来查看运行时间最长的事务。
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;
查看吸尘进度
您可以通过查询 pg_stat_progress_vacuum 视图并使用进程 ID 将其与 pg_stat_activity 视图联接，来检查真空操作的进度。
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;
查看异步查询
如需查看正在异步运行的查询，您可以查询 pg_stat_activity 视图，并过滤出非主进程的查询。
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;
查看阻塞锁定 SQL
您可以通过查询 pg_locks 视图并将其与 pg_stat_activity 视图联接来查看被屏蔽的活动。
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;
确定 work_mem 和 temp_buffers 大小的有效性
如需确定 work_mem 和 temp_buffers 的大小是否符合您的需求，您可以查询 pg_stat_database 视图并检查 postgres.log 文件。使用 pg_stat_database 执行以下查询，如果 temp_files 或 temp_bytes 在两次执行之间有任何增长，则可能需要对 work_mem 或 temp_buffers 进行调整。
SELECT
datname,
temp_files,
temp_bytes
FROM
pg_stat_database;
运行此脚本后，请检查 postgres.log 文件，看看是否使用了临时文件：
LOG: [fd.c:1772] temporary file: path "base/pgsql_tmp/pgsql_tmp4640.1", size 139264
我们的目标是尽可能减少临时文件的创建，而不是完全防止临时文件的创建。这是因为同时设置 work_mem 和 temp_buffers 时，需要在宿主机上的可用内存与需要内存的连接数量之间取得平衡。若要正确设置这些参数，需要了解每个具体工作负载。