--查看当前活动的客户端连接数
 SELECT count(*) FROM pg_stat_activity WHERE NOT pid=pg_backend_pid();    
 
 
 --查询客户端连接的情况
 SELECT pid,case when waiting='f' then 'already get lock,sql executing' when waiting='t' then 'waiting get lock,sql waiting execute' end lock_satus,current_timestamp - least(query_start,xact_start) AS runtime,substr(query,1,25) AS current_query
FROM pg_stat_activity WHERE NOT pid=pg_backend_pid() and state<>'idle' and application_name<>'pg_statsinfod' order by runtime desc






		
--查看持有锁和等待锁的一些信息：
--reltype=0代表其为索引
SELECT locker.pid,pc.relname,locker.mode,locker_act.application_name,least(query_start,xact_start) start_time,locker_act.state,CASE
    WHEN granted='f' THEN
    'wait_lock'
    WHEN granted='t' THEN
    'get_lock'
    END lock_satus,locker_act.query
FROM pg_locks locker,pg_stat_activity locker_act,pg_class pc
WHERE locker.pid=locker_act.pid
        AND NOT locker.pid=pg_backend_pid()
        AND application_name<>'pg_statsinfod'
        AND locker.relation = pc.oid
        AND pc.reltype<>0 --and pc.relname='t'
ORDER BY  runtime desc;














--查询系统中正在执行的或者等待执行的事务
--注意其只是代表事务信息，系统中也有可能存在慢的查询
select pc.relname lock_table,pc.oid,tans.pid,CASE
    WHEN waiting='f' THEN
    'already get lock,sql executing'
    WHEN waiting='t' THEN
    'waiting get lock,sql waiting execute'
    END lock_satus,xact_start) query_start,psa.query
from pg_locks tans,pg_locks pl,pg_class pc,pg_stat_activity psa
where tans.transactionid is NOT null and pc.oid=pl.relation and tans.pid=pl.pid
and tans.pid=psa.pid and pc.reltype<>0
order by runtime desc;




 --查看系统中正在执行的sql与lock_table有关的信息
SELECT locktype,pg_locks.pid,virtualtransaction,transactionid,nspname,relname,mode,granted,CASE
    WHEN granted='f' THEN
    'get_lock'
    WHEN granted='t' THEN
    'wait_lock'
    END lock_satus,cast(date_trunc('second',query_start) AS timestamp) AS query_start,25) AS query
FROM pg_locks LEFT OUTER
JOIN pg_class
    ON (pg_locks.relation = pg_class.oid) LEFT OUTER
JOIN pg_namespace
    ON (pg_namespace.oid = pg_class.relnamespace),pg_stat_activity
WHERE NOT pg_locks.pid=pg_backend_pid()
        AND pg_locks.pid=pg_stat_activity.pid
        AND pg_class.relname='t' --此处进行替换
ORDER BY  query_start;






--查看Postgresql正在执行的sql 
SELECT 
    procpid,start,now() - start AS lap,current_query 
FROM 
    (SELECT 
        backendid,pg_stat_get_backend_pid(S.backendid) AS procpid,pg_stat_get_backend_activity_start(S.backendid) AS start,pg_stat_get_backend_activity(S.backendid) AS current_query 
    FROM 
        (SELECT pg_stat_get_backend_idset() AS backendid) AS S 
    ) AS S,pg_stat_activity pa
WHERE 
   current_query <> '<IDLE>' and  procpid<> pg_backend_pid() and pa.pid=s.procpid and pa.state<>'idle'
ORDER BY 
   lap DESC;
 
procpid：进程id
start：进程开始时间
lap：经过时间
current_query：执行中的sql
怎样停止正在执行的sql
SELECT pg_cancel_backend(进程id);
或者用系统函数
kill -9 进程id;




--查找是否有waiting
ps -ef|grep postgres | grep wait














--查看当前库表和索引的的大小并排序显示前20条
SELECT
nspname,relkind as "type",pg_size_pretty(pg_table_size(C.oid)) AS size,pg_size_pretty(pg_indexes_size(C.oid)) AS idxsize,pg_size_pretty(pg_total_relation_size(C.oid)) as "total"
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE nspname NOT IN ('pg_catalog','information_schema') AND
nspname !~ '^pg_toast' AND
relkind IN ('r','i')
ORDER BY pg_total_relation_size(C.oid) DESC
LIMIT 20;