add chapter 81~93

Author: xiongcc

How to change a Postgres parameter.md

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+# How to change a Postgres parameter
+
+> 我每天都会发布一篇新的 PostgreSQL "howto" 文章。加入我的旅程吧 — 订阅、提供反馈、分享！
+
+如果你需要更改 Postgres 参数 (又称之为 GUC，Grand Unified Configuration) 以实现永久效果，请按照以下步骤操作。
+
+参考文档：[设置参数](https://postgresql.org/docs/current/config-setting.html.)
+
+## 1) 确认是否需要重启
+
+快速检查是否需要重启的两种方法：
+
+- 使用 [postgresqlco.nf](https://postgresqlco.nf/) 并查看 `Restart: xxx` 字段。例如，对于 [max_wal_size](https://postgresqlco.nf/doc/en/param/max_wal_size/)，`Restart: false`，而对于 [shared_buffers](https://postgresqlco.nf/doc/en/param/shared_buffers) 则为 `true`。
+- 检查 `pg_settings` 中的 `context` 字段 — 如果是 `postmaster`，则需要重启，否则不需要 (例外情况：`internal` — 这类参数无法更改)。例如：
+
+```sql
+nik=# select name, context
+from pg_settings
+where name in ('max_wal_size', 'shared_buffers');
+      name      |  context
+----------------+------------
+ max_wal_size   | sighup
+ shared_buffers | postmaster
+(2 rows)
+```
+
+## 2) 进行更改
+
+在 Postgres 配置文件中应用更改 (`postgresql.conf` 或其依赖项，如果使用了 `include` 命令的话)。除非必要，建议避免使用 `ALTER SYSTEM`，以免将来产生混淆 (它会写入 `postgresql.auto.conf`，且可能很容易被忽视；参见[相关讨论](https://postgresql.org/message-id/flat/CA%2BVUV5rEKt2%2BCdC_KUaPoihMu%2Bi5ChT4WVNTr4CD5-xXZUfuQw%40mail.gmail.com))。
+
+## 3) 应用更改
+
+如果需要重启，则重启 Postgres。如果忘记重启，稍后可以在 `pg_settings` 中查看 `pending_restart` 来检测未应用的更改。
+
+如果不需要重启，在超级用户下执行：
+
+```sql
+select pg_reload_conf();
+```
+
+或者使用以下方法之一：
+
+- `pg_ctl reload $PGDATA`
+
+- 发送 `SIGHUP` 信号给 postmaster 进程，例如：
+
+  ~~~bash
+  kill -HUP $(cat "${PGDATA}/postmaster.pid")
+  ~~~
+
+当应用了无需重启的更改时，Postgres 日志中会显示类似以下内容：
+
+```bash
+LOG: received SIGHUP, reloading configuration files
+LOG: parameter "max_wal_size" changed to "2GB"
+```
+
+## 4) 验证更改
+
+使用 `SHOW` 或 `current_setting(...)` 确认更改已生效，例如：
+
+```sql
+nik=# show max_wal_size;
+ max_wal_size
+--------------
+ 2GB
+(1 row)
+```
+
+或者
+
+```sql
+nik=# select current_setting('max_wal_size');
+ current_setting
+-----------------
+ 2GB
+(1 row)
+```
+
+## 额外信息：数据库级、用户级和表级设置
+
+如果 `pg_settings` 中的 `context` 为 `user` 或 `superuser`，那么可以在数据库或用户级别调整设置，例如：
+
+```sql
+alter database verbosedb set log_statement = 'all';
+alter user hero set statement_timeout = 0;
+```
+
+这些结果可以在 `pg_db_role_setting` 中查看：
+
+```sql
+nik=# select * from pg_db_role_setting;
+ setdatabase | setrole |       setconfig
+-------------+---------+-----------------------
+       24580 |       0 | {log_statement=all}
+           0 |   24581 | {statement_timeout=0}
+(2 rows)
+```
+
+当使用 `CREATE TABLE `或 `ALTER TABLE` 时，某些设置还可以在表级别进行调整，参照 [CREATE TABLE / Storage Parameters](https://postgresql.org/docs/current/sql-createtable.html#SQL-CREATETABLE-STORAGE-PARAMETERS)。请注意命名差异：`autovacuum_enabled` 用于启用或禁用特定表的 autovacuum 守护进程，而全局设置名称为 `autovacuum`。
+
+## 我见
+
+在 15 中，还支持了 `\dconfig` 命令，也很方便。
+
+>The \dconfig command can display the parameter settings of the instance. If no option is specified, a list of parameters that have changed from the default values is displayed. If a parameter name is specified, the specific parameter setting value can be checked. Wildcards can be used for parameter names.
+
+~~~sql
+postgres=# \dconfig *mem*
+     List of configuration parameters
+            Parameter             | Value 
+----------------------------------+-------
+ autovacuum_work_mem              | -1
+ dynamic_shared_memory_type       | posix
+ enable_memoize                   | on
+ hash_mem_multiplier              | 2
+ logical_decoding_work_mem        | 64MB
+ maintenance_work_mem             | 64MB
+ min_dynamic_shared_memory        | 0
+ multixact_member_buffers         | 256kB
+ shared_memory_size               | 145MB
+ shared_memory_size_in_huge_pages | 73
+ shared_memory_type               | mmap
+ work_mem                         | 4MB
+(12 rows)
+~~~

How to change ownership of all objects in a database.md

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+# How to change ownership of all objects in a database
+
+>我每天都会发布一篇新的 PostgreSQL "howto" 文章。加入我的旅程吧 — 订阅、提供反馈、分享！
+
+如果需要更改当前数据库中所有对象的所有权，可以使用以下匿名 DO 块 (或从[此处](https://gitlab.com/postgres-ai/database-lab/-/snippets/2075222)粘贴)：
+
+~~~sql
+do $$
+declare
+  new_owner text := 'NEW_OWNER_ROLE_NAME';
+  object_type record;
+  r record;
+  sql text;
+begin
+  -- New owner for all schemas
+  for r in select * from pg_namespace loop
+    sql := format(
+      'alter schema %I owner to %I;',
+      r.nspname,
+      new_owner
+    );
+
+    raise debug 'Execute SQL: %', sql;
+
+    execute sql;
+  end loop;
+
+  -- Various DB objects
+  -- c: composite type
+  -- p: partitioned table
+  -- i: index
+  -- r: table
+  -- v: view
+  -- m: materialized view
+  -- S: sequence
+  for object_type in
+    select
+      unnest('{type,table,table,view,materialized view,sequence}'::text[]) type_name,
+      unnest('{c,p,r,v,m,S}'::text[]) code
+  loop
+    for r in
+      execute format(
+        $sql$
+          select n.nspname, c.relname
+          from pg_class c
+          join pg_namespace n on
+            n.oid = c.relnamespace
+            and not n.nspname in ('pg_catalog', 'information_schema')
+            and c.relkind = %L
+          order by c.relname
+        $sql$,
+        object_type.code
+      )
+    loop
+      sql := format(
+        'alter %s %I.%I owner to %I;',
+        object_type.type_name,
+        r.nspname,
+        r.relname,
+        new_owner
+      );
+
+      raise debug 'Execute SQL: %', sql;
+
+      execute sql;
+    end loop;
+  end loop;
+
+  -- Functions, procedures
+  for r in 
+    select
+      p.proname,
+      n.nspname,
+      pg_catalog.pg_get_function_identity_arguments(p.oid) as args
+    from pg_catalog.pg_namespace as n
+    join pg_catalog.pg_proc as p on p.pronamespace = n.oid
+    where
+      not n.nspname in ('pg_catalog', 'information_schema')
+      and p.proname not ilike 'dblink%' -- We do not want dblink to be involved (exclusion)
+  loop
+    sql := format(
+      'alter function %I.%I(%s) owner to %I', -- todo: check support CamelStyle r.args
+      r.nspname,
+      r.proname,
+      r.args,
+      new_owner
+    );
+
+    raise debug 'Execute SQL: %', sql;
+
+    execute sql;
+  end loop;
+
+  -- Full text search dictionary
+  -- TODO: text search configuration
+  for r in 
+    select * 
+    from pg_catalog.pg_namespace n
+    join pg_catalog.pg_ts_dict d on d.dictnamespace = n.oid
+    where not n.nspname in ('pg_catalog', 'information_schema')
+  loop
+    sql := format(
+      'alter text search dictionary %I.%I owner to %I',
+      r.nspname,
+      r.dictname,
+      new_owner
+    );
+
+    raise debug 'Execute SQL: %', sql;
+
+    execute sql;
+  end loop;
+
+  -- Domains
+  for r in 
+     select typname, nspname
+     from pg_catalog.pg_type
+     join pg_catalog.pg_namespace on pg_namespace.oid = pg_type.typnamespace
+     where typtype = 'd' and not nspname in ('pg_catalog', 'information_schema')
+  loop
+    sql := format(
+      'alter domain %I.%I owner to %I',
+      r.nspname,
+      r.typname,
+      new_owner
+    );
+
+    raise debug 'Execute SQL: %', sql;
+
+    execute sql;
+  end loop;
+end
+$$;
+~~~
+
+不要忘记更改 `new_owner` 的值。
+
+该查询不包括模式 `pg_catalog` 和 `information_schema`，它涵盖：模式对象、表、视图、物化视图、函数、文本搜索字典和域。根据你的 PG 版本，可能还有其他对象需要处理。根据需要调整代码。
+
+要查看调试消息，请在运行之前更改 `client_min_messages`：
+
+~~~sql
+set client_min_messages to debug;
+~~~
+

How to draw frost patterns using SQL ❄.md

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+# How to draw frost patterns using SQL ❄
+
+>我每天都会发布一篇新的 PostgreSQL "howto" 文章。加入我的旅程吧 — 订阅、提供反馈、分享！
+
+此创意和实现最初由Kirill Borovikov (kilor) 完成 — 我只是重新格式化并稍微调整了一下，扩展了字符集。
+
+下面是查询代码：
+
+~~~sql
+with recursive t as (
+  select
+    0 as x,
+    0 as y,
+    '{"{0,0}"}'::text[] as c,
+    0 as i
+
+  union all
+
+  (
+    with z as (
+      select
+        dn.x,
+        dn.y,
+        t.c,
+        t.i
+      from t,
+      lateral (
+        select
+          ((random() * 2 - 1) * 100)::integer as x,
+          ((random() * 2 - 1) * 100)::integer as y
+      ) as p,
+      lateral (
+        select *
+        from (
+          select
+            (unnest::text[])[1]::integer as x,
+            (unnest::text[])[2]::integer as y
+          from unnest(t.c::text[])
+        ) as t
+        order by sqrt((x - p.x) ^ 2 + (y - p.y) ^ 2)
+        limit 1
+      ) as n,
+      lateral (
+        select
+          n.x + dx as x,
+          n.y + dy as y
+        from
+          generate_series(-1, 1) as dx,
+          generate_series(-1, 1) as dy
+        where (dx, dy) <> (0, 0)
+        order by
+          case
+            when (p.x, p.y) = (n.x, n.y) then 0
+            else abs(
+              acos(
+                ((p.x - n.x) * dx + (p.y - n.y) * dy)
+                / sqrt((p.x - n.x) ^ 2 + (p.y - n.y) ^ 2)
+                / sqrt(dx ^ 2 + dy ^ 2)
+              )
+            )
+          end
+        limit 1
+      ) as dn
+    )
+    select
+      z.x,
+      z.y,
+      z.c || array[z.x, z.y]::text,
+      z.i + 1
+    from z
+    where z.i < (1 << 10)
+  )
+),
+map as (
+  select
+    gx as x,
+    gy as y,
+    (
+      select sqrt((gx - T.x) ^ 2 + (gy - T.y) ^ 2) v
+      from t
+      order by v
+      limit 1
+    ) as v
+  from
+    generate_series(-40, 40) as gx,
+    generate_series(-30, 30) as gy
+),
+gr as (
+  select regexp_split_to_array('@%#*+=-:. ', '') as s
+)
+select
+  string_agg(
+    coalesce(s[(v * (array_length(s, 1) - 1))::integer + 1], ' '),
+    ' '
+    order by x
+  ) as frozen
+from
+  (
+    select
+      x,
+      y,
+      v::double precision / max(v) over() as v
+    from map
+  ) as t,
+  gr
+group by y
+order by y;
+~~~
+
+每次它都会绘制一个新的霜花图案，此处是几个例子：
+
+![frozen pattern 1](https://gitlab.com/postgres-ai/postgresql-consulting/postgres-howtos/-/raw/main/files/0082_01.png)
+
+![frozen pattern 2](https://gitlab.com/postgres-ai/postgresql-consulting/postgres-howtos/-/raw/main/files/0082_02.png)
+
+![frozen pattern 3](https://gitlab.com/postgres-ai/postgresql-consulting/postgres-howtos/-/raw/main/files/0082_03.png)
+
+节日快乐🎅