要获得表t的确切行数，我实际运行以下查询
SELECT COUNT(*) AS n FROM t;
有更快的方法吗？
答案 0 :(得分：0)
您可以使用异步例程增量将计数编号添加到其他表中。 或者如果表DML tps很小，可以使用像触发器这样的同步例程。 注意： 当从t表中获取增量数据时，异步例程会引起注意并发问题。 EXP： 触发
postgres=# create table a(id serial4 primary key, info text, crt_time timestamp(0) default now());
NOTICE: CREATE TABLE will create implicit sequence "a_id_seq" for serial column "a.id"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "a_pkey" for table "a"
CREATE TABLE
postgres=# create table cnt_a(id int primary key, cnt int);
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "cnt_a_pkey" for table "cnt_a"
CREATE TABLE
postgres=# insert into cnt_a select generate_series(0,1000),0;
INSERT 0 1001
CREATE OR REPLACE FUNCTION public.tg_insert_a()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
declare
m_id int;
rm numeric;
begin
select max(id),random() into m_id,rm from cnt_a;
update cnt_a set cnt=cnt+1 where id=(rm*m_id)::int;
return null;
end;
$function$;
CREATE OR REPLACE FUNCTION public.tg_delete_a()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
declare
m_id int;
rm numeric;
begin
select max(id),random() into m_id,rm from cnt_a;
update cnt_a set cnt=cnt-1 where id=(rm*m_id)::int;
return null;
end;
$function$;
CREATE OR REPLACE FUNCTION public.tg_truncate_a()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
declare
begin
update cnt_a set cnt=0 where not cnt=0;
return null;
end;
$function$;
create trigger tg1 after insert on a for each row execute procedure tg_insert_a();
create trigger tg2 after delete on a for each row execute procedure tg_delete_a();
create trigger tg3 after truncate on a for each statement execute procedure tg_truncate_a();
pg92@digoal-PowerEdge-R610-> cat insert.sql
insert into a (info) values ('test');
pg92@digoal-PowerEdge-R610-> pgbench -M prepared -r -n -f ./insert.sql -h $PGDATA -p 1919 -U postgres -T 60 -c 16 -j 4 postgres
transaction type: Custom query
scaling factor: 1
query mode: prepared
number of clients: 16
number of threads: 4
duration: 60 s
number of transactions actually processed: 1831418
tps = 30514.831839 (including connections establishing)
tps = 30522.057886 (excluding connections establishing)
statement latencies in milliseconds:
0.522411 insert into a (info) values ('test');
postgres=# select count(*) from a;
count
---------
1755964
(1 row)
Time: 285.491 ms
postgres=# select sum(cnt) from cnt_a ;
sum
---------
1755964
(1 row)
Time: 0.689 ms
async count exp：
- #TEST TABLE：
创建表日志 （ id序列主键， xid int8默认txid_current（）不为null， c1 int not null， c2 int not null， c3 int not null， c4文本不为空， crt_time timestamp默认现在（） ）; 在log（xid）上创建索引idx_log_1;
-- # COUTN TABLE
create table log_c1_cnt_day (c1 int, cnt int8, stat_time text, primary key(c1,stat_time));
create table log_c1_cnt_week (c1 int, cnt int8, stat_time text, primary key(c1,stat_time));
create table log_c1_cnt_month (c1 int, cnt int8, stat_time text, primary key(c1,stat_time));
create table log_c1_cnt_year (c1 int, cnt int8, stat_time text, primary key(c1,stat_time));
-- # COUNT TABLE 2
create table log_c2_c3_cnt_day (c2 int, c3 int, cnt int8, stat_time text, primary key(c2,c3,stat_time));
create table log_c2_c3_cnt_week (c2 int, c3 int, cnt int8, stat_time text, primary key(c2,c3,stat_time));
create table log_c2_c3_cnt_month (c2 int, c3 int, cnt int8, stat_time text, primary key(c2,c3,stat_time));
create table log_c2_c3_cnt_year (c2 int, c3 int, cnt int8, stat_time text, primary key(c2,c3,stat_time));
-- TEST DATA
insert into log (c1,c2,c3,c4) values (1,1,1,1);
insert into log (c1,c2,c3,c4) values (2,2,2,2);
--
digoal=# select * from log;
id | xid | c1 | c2 | c3 | c4 | crt_time
----+-----------+----+----+----+----+----------------------------
1 | 480125659 | 1 | 1 | 1 | 1 | 2013-04-21 20:55:45.907713
2 | 480125660 | 2 | 2 | 2 | 2 | 2013-04-21 20:55:46.286933
(2 rows)
- ＃aysnc count function
create table log_read
(
tablename name not null,
xid int8 not null,
xip int8[],
xip_res int8[],
mod_time timestamp,
primary key (tablename)
);
insert into log_read values ('log', 0, null, null, now());
create or replace function analyze_log(v_limit int) returns void as $$
declare
v_advisory_xact_lock int8 := null;
v_xid_snap txid_snapshot := null;
v_xmin int8 := null;
v_xmax int8 := null;
v_xip int8[] := null;
v_log_read_log_xid int8 := null;
v_log_read_log_xid_update int8 := null;
v_log_read_log_xip int8[] := null;
v_log_read_log_xip_do int8[] := null;
v_log_read_log_xip_update int8[] := null;
v_log_read_log_xip_res int8[] := null;
v_log_read_log_xip_res_update int8[] := null;
v_log log[] := null;
v_log_doxip log[] := null;
begin
if v_limit <=0 then
raise notice 'please ensure v_limit > 0 .';
return;
end if;
v_advisory_xact_lock := 1;
if not pg_try_advisory_xact_lock(v_advisory_xact_lock) then
raise notice 'Another function is calling, this call will exit.';
return;
end if;
v_xid_snap := txid_current_snapshot();
v_xmin := txid_snapshot_xmin(v_xid_snap);
v_xmax := txid_snapshot_xmax(v_xid_snap);
select array_agg(t) into v_xip from txid_snapshot_xip(v_xid_snap) g(t);
select xid,xip,xip_res into v_log_read_log_xid,v_log_read_log_xip,v_log_read_log_xip_res from log_read where tablename='log';
if not found then
raise notice 'log_read no log entry. please add it in log_read table first.';
return;
end if;
select max(xid) into v_log_read_log_xid_update from (select xid from log where xid > v_log_read_log_xid and xid < v_xmax and xid not in (select * from unnest(v_xip) union all select * from unnest(v_log_read_log_xip_res)) order by xid limit v_limit) t;
if v_log_read_log_xid_update is not null then
raise notice '取log1';
select array_agg(log) into v_log from (select log from log where xid > v_log_read_log_xid and xid<=v_log_read_log_xid_update and xid not in (select * from unnest(v_xip) union all select * from unnest(v_log_read_log_xip_res)) order by xid) t;
else
v_log_read_log_xid_update := v_log_read_log_xid;
end if;
select array_agg(i) into v_log_read_log_xip_do from (select * from unnest(v_log_read_log_xip) i except select * from unnest(v_xip))t where i is not null;
select array_agg(i) into v_log_read_log_xip_update from
( select i from (select * from unnest(v_log_read_log_xip) i union all select * from unnest(v_xip)
except select * from unnest(v_log_read_log_xip_do)) t where i is not null group by i ) t;
select array_agg(i) into v_log_read_log_xip_res_update from (select * from unnest(v_log_read_log_xip_res) i union select * from unnest(v_log_read_log_xip) union select * from unnest(v_xip))t where i>v_log_read_log_xid_update;
select array_agg(log) into v_log_doxip from log where xid in (select * from unnest(v_log_read_log_xip_do));
update log_read set
xip=v_log_read_log_xip_update,
xid=v_log_read_log_xid_update,
xip_res=v_log_read_log_xip_res_update,
mod_time=now()
where tablename='log';
-- raise notice 'log_read.oldxip(log): %.', v_log_read_log_xip;
-- raise notice 'log_read.newxip(log): %.', v_log_read_log_xip_update;
-- raise notice 'log_read.newxipres(log): %.', v_log_read_log_xip_res_update;
perform stat_log_c1(v_log);
perform stat_log_c1(v_log_doxip);
return;
end;
$$ language plpgsql;
CREATE OR REPLACE FUNCTION public.stat_log_c1(v_log log[])
RETURNS void
LANGUAGE plpgsql
AS $function$
declare
v_stat_time text;
v_c1 int;
v_cnt int8;
begin
for v_stat_time, v_c1, v_cnt in select to_char(crt_time, 'yyyymmdd'), c1 , count(*) from (select ((unnest(v_log)::log)).*) t group by to_char(crt_time, 'yyyymmdd'), c1 loop
perform 1 from log_c1_cnt_day where c1=v_c1 and stat_time=v_stat_time;
if not found then
insert into log_c1_cnt_day(c1, cnt, stat_time) values (v_c1, v_cnt, v_stat_time);
else
update log_c1_cnt_day set cnt=cnt+v_cnt where c1=v_c1 and stat_time=v_stat_time;
end if;
end loop;
end;
$function$;
truncate log;
truncate log_c1_cnt_day;
update log_read set xid=0, xip=null, xip_res=null;
-- pgbench script
cat ins.sql
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
-- # pgbench
pg92@digoal-PowerEdge-R610-> pgbench -M prepared -f ./ins.sql -r -n -h $PGDATA -U postgres -T 60 -c 8 -j 2
transaction type: Custom query
scaling factor: 1
query mode: prepared
number of clients: 8
number of threads: 2
duration: 60 s
number of transactions actually processed: 2887271
tps = 48121.007692 (including connections establishing)
tps = 48131.903512 (excluding connections establishing)
statement latencies in milliseconds:
0.164881 insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
pg92@digoal-PowerEdge-R610-> cat analyze.sh
#!/bin/bash
for ((i=0;i<100;i++))
do
psql -c "select * from analyze_log(1);"
psql -c "select * from analyze_log(1000000);"
done
# 调用analyze.sh
digoal=# select c1,count(*),to_char(crt_time,'yyyymmdd') from log group by c1,to_char(crt_time,'yyyymmdd') order by c1;
c1 | count | to_char
----+--------+----------
0 | 140071 | 20130421
1 | 282303 | 20130421
2 | 281499 | 20130421
3 | 281339 | 20130421
4 | 282008 | 20130421
5 | 281871 | 20130421
6 | 282954 | 20130421
7 | 281855 | 20130421
8 | 281560 | 20130421
9 | 281516 | 20130421
10 | 140456 | 20130421
(11 rows)
digoal=# select * from log_c1_cnt_day where cnt<>0 order by c1;
c1 | cnt | stat_time
----+--------+-----------
0 | 140071 | 20130421
1 | 282303 | 20130421
2 | 281499 | 20130421
3 | 281339 | 20130421
4 | 282008 | 20130421
5 | 281871 | 20130421
6 | 282954 | 20130421
7 | 281855 | 20130421
8 | 281560 | 20130421
9 | 281516 | 20130421
10 | 140456 | 20130421
(11 rows)
cat ins.sql
begin;
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
end;
begin;
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
rollback;
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
insert into log (c1,c2,c3,c4) values(round(random()*10),1,2,3);
-- # pgbench
pg92@digoal-PowerEdge-R610-> pgbench -M prepared -f ./ins.sql -r -n -h $PGDATA -U postgres -T 60 -c 8 -j 2
transaction type: Custom query
scaling factor: 1
query mode: prepared
number of clients: 8
number of threads: 2
duration: 60 s
number of transactions actually processed: 100862
tps = 1680.570420 (including connections establishing)
tps = 1680.946330 (excluding connections establishing)
statement latencies in milliseconds:
pg92@digoal-PowerEdge-R610-> cat analyze.sh
#!/bin/bash
for ((i=0;i<100;i++))
do
psql -c "select * from analyze_log(1);"
psql -c "select * from analyze_log(1000000);"
done
digoal=# select c1,count(*),to_char(crt_time,'yyyymmdd') from log group by c1,to_char(crt_time,'yyyymmdd') order by c1;
c1 | count | to_char
----+--------+----------
0 | 245002 | 20130426
1 | 491034 | 20130426
2 | 489717 | 20130426
3 | 490628 | 20130426
4 | 490064 | 20130426
5 | 490393 | 20130426
6 | 490893 | 20130426
7 | 490081 | 20130426
8 | 490180 | 20130426
9 | 490659 | 20130426
10 | 245860 | 20130426
(11 rows)
digoal=# select * from log_c1_cnt_day where cnt<>0 order by c1;
c1 | cnt | stat_time
----+--------+-----------
0 | 245002 | 20130426
1 | 491034 | 20130426
2 | 489717 | 20130426
3 | 490628 | 20130426
4 | 490064 | 20130426
5 | 490393 | 20130426
6 | 490893 | 20130426
7 | 490081 | 20130426
8 | 490180 | 20130426
9 | 490659 | 20130426
10 | 245860 | 20130426
(11 rows)