PostgreSQL 13:索引并行vacuum

postgres=# \h vacuum
Command:     VACUUM
Description: garbage-collect and optionally analyze a database
Syntax:
VACUUM [ ( option [, ...] ) ] [ table_and_columns [, ...] ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ table_and_columns [, ...] ]
where option can be one of:
    FULL [ boolean ]
    FREEZE [ boolean ]
    VERBOSE [ boolean ]
    ANALYZE [ boolean ]
    DISABLE_PAGE_SKIPPING [ boolean ]
    SKIP_LOCKED [ boolean ]
    INDEX_CLEANUP [ boolean ]
    TRUNCATE [ boolean ]
    PARALLEL integer
and table_and_columns is:
    table_name [ ( column_name [, ...] ) ]
URL: https://www.postgresql.org/docs/devel/sql-vacuum.html

postgres=# create table t1 as select i as a, i::text as b, now() as c from generate_series(1,3000000) i;
SELECT 3000000
postgres=# create index i1 on t1(a);
CREATE INDEX
postgres=# 
postgres=# create index i2 on t1(b);
CREATE INDEX
postgres=# create index i3 on t1(c);
CREATE INDEX

postgres=# update t1 set a=5,b='ccc',c=now() where mod(a,5)=0;
UPDATE 600000
postgres=# vacuum (parallel 4) t1;
VACUUM

postgres 16688 15925 13 07:30 ?        00:01:07 postgres: postgres postgres [local] VACUUM
postgres 19184 15925  0 07:39 ?        00:00:00 postgres: parallel worker for PID 16688   
postgres 19185 15925  0 07:39 ?        00:00:00 postgres: parallel worker for PID 16688 

postgres=# vacuum (parallel -4) t1;
ERROR:  parallel vacuum degree must be between 0 and 1024
LINE 1: vacuum (parallel -4) t1;

postgres=# vacuum (parallel 4, verbose true) t1;
INFO:  vacuuming "public.t1"
INFO:  launched 2 parallel vacuum workers for index vacuuming (planned: 2)
INFO:  scanned index "i2" to remove 600000 row versions by parallel vacuum worker
DETAIL:  CPU: user: 0.24 s, system: 0.06 s, elapsed: 0.89 s
INFO:  scanned index "i1" to remove 600000 row versions
DETAIL:  CPU: user: 0.17 s, system: 0.10 s, elapsed: 1.83 s
INFO:  scanned index "i3" to remove 600000 row versions by parallel vacuum worker
DETAIL:  CPU: user: 0.16 s, system: 0.14 s, elapsed: 1.69 s
INFO:  scanned index "i4" to remove 600000 row versions by parallel vacuum worker
DETAIL:  CPU: user: 0.25 s, system: 0.09 s, elapsed: 1.17 s
INFO:  "t1": removed 600000 row versions in 20452 pages
DETAIL:  CPU: user: 0.17 s, system: 0.16 s, elapsed: 1.43 s
INFO:  index "i1" now contains 3000000 row versions in 14308 pages
DETAIL:  600000 index row versions were removed.
1852 index pages have been deleted, 640 are currently reusable.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO:  index "i2" now contains 3000000 row versions in 14305 pages
DETAIL:  600000 index row versions were removed.
1851 index pages have been deleted, 640 are currently reusable.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO:  index "i3" now contains 3000000 row versions in 14326 pages
DETAIL:  600000 index row versions were removed.
3941 index pages have been deleted, 1603 are currently reusable.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO:  index "i4" now contains 3000000 row versions in 23391 pages
DETAIL:  600000 index row versions were removed.
5527 index pages have been deleted, 2246 are currently reusable.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO:  "t1": found 600000 removable, 3000000 nonremovable row versions in 21835 out of 22072 pages
DETAIL:  0 dead row versions cannot be removed yet, oldest xmin: 499
There were 132 unused item identifiers.
Skipped 0 pages due to buffer pins, 237 frozen pages.
0 pages are entirely empty.
CPU: user: 0.75 s, system: 0.36 s, elapsed: 5.07 s.
INFO:  vacuuming "pg_toast.pg_toast_16392"
INFO:  index "pg_toast_16392_index" now contains 0 row versions in 1 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
INFO:  "pg_toast_16392": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet, oldest xmin: 499
There were 0 unused item identifiers.
Skipped 0 pages due to buffer pins, 0 frozen pages.
0 pages are entirely empty.
CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s.
VACUUM