UUID V1 和 V4 在顺序插入和删除后显着膨胀。与串行和时间 BTree（不会膨胀）相比，为什么会这样？

Question

我试图了解在大量插入和删除后删除对表和索引膨胀的影响。插入和删除遵循相当严格的模式：首先，记录按顺序插入，在下一个时间段（通常为五年）内很少（或几乎从不）更新，一旦超过此阈值（五年）就删除。这是许多企业软件系统中的典型场景，出于合规性原因需要保留记录。

数据库 (PostgreSQL 9.6.5) 以非常标准的配置运行（增加了一些参数以进行快速查询和维护处理）。

我正在尝试模拟和分析表和（典型）索引的膨胀。在概念层面上，（1）创建一个表，（2）分析它（3）插入记录（4）再次分析它，（5）删除一半的记录（6）分析它（7）再次分析它，（ 8) 再次插入已删除记录的数量 (9) 分析它并 (10) 再次分析它和 (11) 检查索引和表是否膨胀。

完整的SQL代码如下：

set LC_MESSAGES ='C'

create extension "uuid-ossp"

drop table v1;
create table v1 (
    id serial primary key, 
    id_uuid_v1 uuid default uuid_generate_v1(), 
    id_uuid_v4 uuid default uuid_generate_v4(), 
    t timestamp with time zone default clock_timestamp(),
    name varchar
);
create index ix_v1_uuid on v1 (id_uuid_v1);
create index ix_v4_uuid on v1 (id_uuid_v4);
create index ix_v1_t on v1 (t);

vacuum (verbose, analyze, freeze) v1;

select pg_size_pretty(pg_relation_size('v1')), count(*)
from v1;

-- emtpy the table
-- truncate v1;

-- generate 100K records
INSERT INTO v1 (name)
SELECT x.id
  FROM generate_series(1,100000) AS x(id);

vacuum (verbose, analyze, freeze) v1;
vacuum (verbose, analyze, freeze) v1;

-- delete half of the records
delete from v1
where id <= (select avg(id) from v1);

-- free the pages
vacuum (verbose, analyze, freeze) v1;
vacuum (verbose, analyze, freeze) v1;
--vacuum full v1;

-- generate the number another half of the records
with c as (
  select count(*) c
  from v1
)
INSERT INTO v1 (name)
SELECT generate_series(0,c.c-1)
from c;

-- updated statistics
vacuum (verbose, analyze, freeze) v1;

select *
from v1
limit 10

在此之后报告的膨胀是：

对于表

  schemaname | tblname | bloat_ratio | bloat_size | bloat_size_pretty | real_size | real_size_pretty |        ?column?
------------+---------+-------------+------------+-------------------+-----------+------------------+------------------------
 public     | v1      |         0.2 |      16384 | 16 kB             |   8445952 | 8248 kB          | VACUUM FULL public.v1;

对于索引：

 schemaname | tblname |  idxname   | bloat_ratio | bloat_size | bloat_size_pretty | real_size | real_size_pretty |             ?column?
------------+---------+------------+-------------+------------+-------------------+-----------+------------------+----------------------------------
 public     | v1      | ix_v1_uuid |        31.9 |    1466368 | 1432 kB           |   4603904 | 4496 kB          | REINDEX INDEX public.ix_v1_uuid;
 public     | v1      | ix_v4_uuid |        29.7 |    1327104 | 1296 kB           |   4464640 | 4360 kB          | REINDEX INDEX public.ix_v4_uuid;
 public     | v1      | ix_v1_t    |         0.4 |       8192 | 8192 bytes        |   2260992 | 2208 kB          | REINDEX INDEX public.ix_v1_t;
 public     | v1      | v1_pkey    |         0.4 |       8192 | 8192 bytes        |   2260992 | 2208 kB          | REINDEX INDEX public.v1_pkey;

我的期望是：

• 串行 btree 不会膨胀（已确认）
• 时间 btree 不会膨胀（已确认）
• V1 UUID btree 不会膨胀（与预期相反）
• V4 UUID btree 会膨胀（已确认）
• V4 膨胀大于 V1 膨胀（与预期确认相反）

更新（期望的原因）：

• 串行 Btree 不会因顺序删除而膨胀，因为 btree 中的页面会顺序删除：删除的不仅仅是页面中的几条记录，而是释放了一个完整的页面。此页面稍后会在插入插入时重复使用。
• 类似的论据遵循时间 btree：b 树中的时间值存储为浮点数。这些浮动被顺序删除，整个页面被释放，标记为被真空释放，然后被插入重用。
• V1 UUID btree 实际上是遵循以下结构的 128 位：[time_now][mac 地址的哈希]（检查下表）。删除也需要是顺序的，需要释放一个完整的块（实际上可以从真空详细中看到一些）。V1 索引实际上应该表现得类似于时间索引（效果很好，即不会膨胀）。
• V4 UUID 是一个随机的 128 ID。删除一半的记录会使页面看起来像一个筛子。删除后，所有页面将包含一半的记录为空，即膨胀。
• 重新插入膨胀的 V4 索引会减少膨胀（期望列表中的最后一点）。这在某种程度上是可以理解的，但由于 V1 不应膨胀，因此 V1 索引必须表现得更好。

到底是怎么回事？？！

附加信息来自vacuum verboze analyze：

在任何事情之前

INFO:  vacuuming "public.v1"
INFO:  index "v1_pkey" 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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_uuid" 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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v4_uuid" 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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_t" 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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "v1": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  vacuuming "pg_toast.pg_toast_1701065"
INFO:  index "pg_toast_1701065_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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_toast_1701065": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "public.v1"
INFO:  "v1": scanned 0 of 0 pages, containing 0 live rows and 0 dead rows; 0 rows in sample, 0 estimated total rows

Query returned successfully with no result in 37 msec.

插入后

INFO:  vacuuming "public.v1"
INFO:  index "v1_pkey" now contains 100000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_uuid" now contains 100000 row versions in 388 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v4_uuid" now contains 100000 row versions in 534 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_t" now contains 100000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "v1": found 0 removable, 100000 nonremovable row versions in 1031 out of 1031 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.01u sec elapsed 0.01 sec.
INFO:  vacuuming "pg_toast.pg_toast_1701082"
INFO:  index "pg_toast_1701082_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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_toast_1701082": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "public.v1"
INFO:  "v1": scanned 1031 of 1031 pages, containing 100000 live rows and 0 dead rows; 30000 rows in sample, 100000 estimated total rows
Query returned successfully with no result in 179 msec.

删除后，第一次运行真空

INFO:  vacuuming "public.v1"
INFO:  scanned index "v1_pkey" to remove 50000 row versions
DETAIL:  CPU 0.00s/0.01u sec elapsed 0.00 sec
INFO:  scanned index "ix_v1_uuid" to remove 50000 row versions
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec
INFO:  scanned index "ix_v4_uuid" to remove 50000 row versions
DETAIL:  CPU 0.00s/0.01u sec elapsed 0.01 sec
INFO:  scanned index "ix_v1_t" to remove 50000 row versions
DETAIL:  CPU 0.00s/0.01u sec elapsed 0.01 sec
INFO:  "v1": removed 50000 row versions in 516 pages
DETAIL:  CPU 0.00s/0.00u sec elapsed 0.00 sec
INFO:  index "v1_pkey" now contains 50000 row versions in 276 pages
DETAIL:  50000 index row versions were removed.
136 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_uuid" now contains 50000 row versions in 388 pages
DETAIL:  50000 index row versions were removed.
191 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v4_uuid" now contains 50000 row versions in 534 pages
DETAIL:  50000 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_t" now contains 50000 row versions in 276 pages
DETAIL:  50000 index row versions were removed.
136 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "v1": found 50000 removable, 142 nonremovable row versions in 517 out of 1031 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.04u sec elapsed 0.05 sec.
INFO:  vacuuming "pg_toast.pg_toast_1701082"
INFO:  index "pg_toast_1701082_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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_toast_1701082": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "public.v1"
INFO:  "v1": scanned 1031 of 1031 pages, containing 50000 live rows and 0 dead rows; 30000 rows in sample, 50000 estimated total rows
Query returned successfully with no result in 116 msec.

二次真空

INFO:  vacuuming "public.v1"
INFO:  index "v1_pkey" now contains 50000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
136 index pages have been deleted, 136 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_uuid" now contains 50000 row versions in 388 pages
DETAIL:  0 index row versions were removed.
191 index pages have been deleted, 191 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v4_uuid" now contains 50000 row versions in 534 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_t" now contains 50000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
136 index pages have been deleted, 136 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "v1": found 0 removable, 90 nonremovable row versions in 1 out of 1031 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.02 sec.
INFO:  vacuuming "pg_toast.pg_toast_1701082"
INFO:  index "pg_toast_1701082_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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_toast_1701082": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "public.v1"
INFO:  "v1": scanned 1031 of 1031 pages, containing 50000 live rows and 0 dead rows; 30000 rows in sample, 50000 estimated total rows
Query returned successfully with no result in 272 msec.

再次插入后，第一次抽真空

INFO:  vacuuming "public.v1"
INFO:  index "v1_pkey" now contains 100000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_uuid" now contains 100000 row versions in 562 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v4_uuid" now contains 100000 row versions in 545 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_t" now contains 100000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "v1": found 0 removable, 50142 nonremovable row versions in 517 out of 1031 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  vacuuming "pg_toast.pg_toast_1701082"
INFO:  index "pg_toast_1701082_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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_toast_1701082": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "public.v1"
INFO:  "v1": scanned 1031 of 1031 pages, containing 100000 live rows and 0 dead rows; 30000 rows in sample, 100000 estimated total rows
Query returned successfully with no result in 180 msec.

二次真空

INFO:  vacuuming "public.v1"
INFO:  index "v1_pkey" now contains 100000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_uuid" now contains 100000 row versions in 562 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v4_uuid" now contains 100000 row versions in 545 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  index "ix_v1_t" now contains 100000 row versions in 276 pages
DETAIL:  0 index row versions were removed.
0 index pages have been deleted, 0 are currently reusable.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "v1": found 0 removable, 90 nonremovable row versions in 1 out of 1031 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  vacuuming "pg_toast.pg_toast_1701082"
INFO:  index "pg_toast_1701082_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 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  "pg_toast_1701082": found 0 removable, 0 nonremovable row versions in 0 out of 0 pages
DETAIL:  0 dead row versions cannot be removed yet.
There were 0 unused item pointers.
Skipped 0 pages due to buffer pins.
0 pages are entirely empty.
CPU 0.00s/0.00u sec elapsed 0.00 sec.
INFO:  analyzing "public.v1"
INFO:  "v1": scanned 1031 of 1031 pages, containing 100000 live rows and 0 dead rows; 30000 rows in sample, 100000 estimated total rows
Query returned successfully with no result in 158 msec.

样本数据

   id   |              id_uuid_v1              |              id_uuid_v4              |               t               | name
--------+--------------------------------------+--------------------------------------+-------------------------------+------
 100001 | 21515a0a-f07c-11e7-9a90-509a4c44f517 | 18632922-249f-439f-9b54-6cb29f8c97a2 | 2018-01-03 12:49:18.368387+01 | 0
 100002 | 2152bad0-f07c-11e7-9b55-509a4c44f517 | 0ba51425-7225-416f-a79f-b2db0ed23155 | 2018-01-03 12:49:18.377475+01 | 1
 100003 | 2152bad1-f07c-11e7-a7a0-509a4c44f517 | 486fb3ae-204f-4c8a-8171-7089b2c9d946 | 2018-01-03 12:49:18.377699+01 | 2
 100004 | 2152ce26-f07c-11e7-8172-509a4c44f517 | 83ec70ea-69bd-45a7-800c-eac558521e19 | 2018-01-03 12:49:18.3779+01   | 3
 100005 | 2152ce27-f07c-11e7-800d-509a4c44f517 | cc5f356f-589d-4bcd-b627-b731e496c56d | 2018-01-03 12:49:18.378173+01 | 4
 100006 | 2152e1b8-f07c-11e7-b628-509a4c44f517 | 495e4216-76ca-4806-90d8-d0cc1d8ea53f | 2018-01-03 12:49:18.378373+01 | 5
 100007 | 2152e1b9-f07c-11e7-90d9-509a4c44f517 | aaa824bf-34e1-4ec9-a589-b86ad77d9df0 | 2018-01-03 12:49:18.37857+01  | 6
 100008 | 2152f54a-f07c-11e7-a58a-509a4c44f517 | 0474fd4a-6f2c-4717-a59d-d6c6337eabee | 2018-01-03 12:49:18.378765+01 | 7
 100009 | 2152f54b-f07c-11e7-a59e-509a4c44f517 | 5f416afa-7a4f-4692-bbe1-991a99cc8e25 | 2018-01-03 12:49:18.378958+01 | 8
 100010 | 2152f54c-f07c-11e7-bbe2-509a4c44f517 | f32e5a17-40b1-4ab0-af41-a3557ff4fb3e | 2018-01-03 12:49:18.379249+01 | 9

检查索引的代码：

CREATE OR REPLACE VIEW public.bloat_inx AS 
 SELECT o.schemaname::text AS schemaname,
    o.tblname::text AS tblname,
    o.idxname::text AS idxname,
    round(o.bloat_ratio::numeric, 1) AS bloat_ratio,
    o.bloat_size::numeric AS bloat_size,
    pg_size_pretty(o.bloat_size::bigint) AS bloat_size_pretty,
    o.relpages * 8 * 1024::bigint AS real_size,
    pg_size_pretty(o.relpages * 8 * 1024::bigint) AS real_size_pretty,
    ((('REINDEX INDEX '::text || o.schemaname::text) || '.'::text) || o.idxname::text) || ';'::text
   FROM ( SELECT current_database() AS current_database,
            sub.nspname AS schemaname,
            sub.tblname,
            sub.idxname,
            sub.bs * (sub.relpages::double precision - sub.est_pages)::bigint::numeric AS extra_size,
            100::double precision * (sub.relpages::double precision - sub.est_pages) / sub.relpages::double precision AS extra_ratio,
            sub.fillfactor,
            sub.bs::double precision * (sub.relpages::double precision - sub.est_pages_ff) AS bloat_size,
            100::double precision * (sub.relpages::double precision - sub.est_pages_ff) / sub.relpages::double precision AS bloat_ratio,
            sub.relpages,
            sub.is_na
           FROM ( SELECT COALESCE(1::double precision + ceil(s2.reltuples / floor((s2.bs - s2.pageopqdata::numeric - s2.pagehdr::numeric)::double precision / (4::numeric + s2.nulldatahdrwidth)::double precision)), 0::double precision) AS est_pages,
                    COALESCE(1::double precision + ceil(s2.reltuples / floor(((s2.bs - s2.pageopqdata::numeric - s2.pagehdr::numeric) * s2.fillfactor::numeric)::double precision / (100::double precision * (4::numeric + s2.nulldatahdrwidth)::double precision))), 0::double precision) AS est_pages_ff,
                    s2.bs,
                    s2.nspname,
                    s2.table_oid,
                    s2.tblname,
                    s2.idxname,
                    s2.relpages,
                    s2.fillfactor,
                    s2.is_na
                   FROM ( SELECT s1.maxalign,
                            s1.bs,
                            s1.nspname,
                            s1.tblname,
                            s1.idxname,
                            s1.reltuples,
                            s1.relpages,
                            s1.relam,
                            s1.table_oid,
                            s1.fillfactor,
                   

    

Answer 1

当您使用顺序 UUID 变体时，UUID 索引会变得更加高效。一段时间以来，出现了许多或多或少与 RFC 4122 兼容的顺序 UUID 变体（如 ULID、KSUID 和 XID）。然而，现在也有人建议使用 UUIDv6、UUIDv7 和 UUIDv8 来扩展 RFC 4122，这三个文件都可以按时间戳部分进行字节排序。

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我最喜欢的 UUIDv7 实现是pg_uuidv7. UUIDv7 基于 Unix 时间戳，但具有足够大小的随机块以避免冲突（在实现pg_uuidv7\xe2\x80\x93 中，该块\n可能是随机的）。如果您想要进行比较，我最近对截至 2023 年第二季度的PostgreSQL 顺序 UUID 情况进行了调查。

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