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Peter's questions

Martin Hope
Peter
Asked: 2024-05-15 16:00:03 +0800 CST
  • 5

Oracle 有全局索引，Postgres 没有。到目前为止，一切都很好。

然后，Oracle 具有本地前缀索引和非前缀索引，并且即使在 V19 中，Oracle 也充分利用了这种差异：Oracle Docs

我真的不明白为什么 Oracle 会产生这种差异，我只能用“惰性编程”向自己解释，但这不是这里的问题。

我的问题是：除了这些明显的原因之外，在 postgres 中为索引添加前缀是否有用：

  • 将分区键作为索引中的前缀对您很有用，因为索引中的排序对您很有用
  • 将分区键作为索引中的前缀对您很有用，因为分区键可以有许多不同的值
postgresql
Martin Hope
Peter
Asked: 2024-04-18 15:46:46 +0800 CST
  • 6

pg_log_backend_memory_contexts(PG14.1) 下面是PID的输出，其中pg_proctab()表示。我添加了一些点，以便更轻松地读取大量数字，并且匿名了一些内容。rss216MB

我不明白：

  • 为什么 TopMemoryContext 只有 5MB 但总共有 100MB？
  • CacheMemoryContext 为 69MB，但其中 44MB 是空闲的，25MB 已使用。这 25MB 里有什么？这不正是 pg_log_backend_memory_contexts 应该告诉我的（但没有）吗？所有“2 级”条目的大小都不到 25MB。
  • 在会话有效期间，这些免费的 44MB 是否会返回到系统？
  • 当我终止会话时，它会释放 216MB RAM（pc_proctab 编号）或 100MB（pg_log_backend_memory_contexts 编号）还是其他数字？
logging memory contexts of PID 15744
level: 0; TopMemoryContext: 4.264.856 total in 104 blocks; 2.074.448 free (8510 chunks); 2190408 used
level: 1; pgstat TabStatusArray lookup hash table: 65536 total in 4 blocks; 4672 free (11 chunks); 60864 used
level: 1; RdsSuperUserCache: 8192 total in 1 blocks; 552 free (0 chunks); 7640 used
level: 1; PL/pgSQL function: 8192 total in 1 blocks; 3792 free (1 chunks); 4400 used: get_date_to_char(timestamp without time zone,character varying)
level: 1; PL/pgSQL function: 16384 total in 2 blocks; 7032 free (5 chunks); 9352 used: get_number_to_char(numeric,character varying)
level: 1; PL/pgSQL function: 8192 total in 1 blocks; 3824 free (3 chunks); 4368 used: get_to_number(character varying,character varying)
level: 1; PL/pgSQL function: 8192 total in 1 blocks; 4504 free (1 chunks); 3688 used: <FUNCTION>
level: 1; PL/pgSQL function: 16384 total in 2 blocks; 6616 free (4 chunks); 9768 used: <FUNCTION2>
level: 1; Sequence values: 8192 total in 1 blocks; 1576 free (0 chunks); 6616 used
level: 1; Btree proof lookup cache: 8192 total in 1 blocks; 552 free (0 chunks); 7640 used
level: 1; PL/pgSQL function: 16384 total in 2 blocks; 5752 free (5 chunks); 10632 used: get_date_interval(character varying,numeric)
level: 1; PL/pgSQL function: 32768 total in 3 blocks; 16608 free (5 chunks); 16160 used: <FUNCTION3>
level: 1; Operator lookup cache: 24576 total in 2 blocks; 10752 free (3 chunks); 13824 used
level: 1; RI compare cache: 16384 total in 2 blocks; 6656 free (3 chunks); 9728 used
level: 1; RI query cache: 8192 total in 1 blocks; 1576 free (0 chunks); 6616 used
level: 1; RI constraint cache: 40648 total in 2 blocks; 2616 free (0 chunks); 38032 used
level: 1; PL/pgSQL function: 8192 total in 1 blocks; 4592 free (1 chunks); 3600 used: get_systimestamp()
level: 1; Type information cache: 24376 total in 2 blocks; 2616 free (0 chunks); 21760 used
level: 1; PLpgSQL cast cache: 8192 total in 1 blocks; 1576 free (0 chunks); 6616 used
level: 1; PLpgSQL cast expressions: 8192 total in 1 blocks; 1576 free (0 chunks); 6616 used
level: 1; PL/pgSQL function: 16384 total in 2 blocks; 5992 free (4 chunks); 10392 used: <FUNCTION4>
level: 1; Function stat entries: 16384 total in 2 blocks; 6640 free (2 chunks); 9744 used
level: 1; CFuncHash: 8192 total in 1 blocks; 552 free (0 chunks); 7640 used
level: 1; Rendezvous variable hash: 8192 total in 1 blocks; 552 free (0 chunks); 7640 used
level: 1; PLpgSQL function hash: 24528 total in 2 blocks; 2616 free (0 chunks); 21912 used
level: 1; Prepared Queries: 16384 total in 2 blocks; 6656 free (3 chunks); 9728 used
level: 1; TableSpace cache: 8192 total in 1 blocks; 2088 free (0 chunks); 6104 used
level: 1; RowDescriptionContext: 57400 total in 3 blocks; 24272 free (7 chunks); 33128 used
level: 1; MessageContext: 8192 total in 1 blocks; 6888 free (1 chunks); 1304 used
level: 1; Operator class cache: 8192 total in 1 blocks; 552 free (0 chunks); 7640 used
level: 1; smgr relation table: 2.097.152 total in 9 blocks; 269224 free (33 chunks); 1827928 used
level: 1; TransactionAbortContext: 32768 total in 1 blocks; 32504 free (0 chunks); 264 used
level: 1; Portal hash: 8192 total in 1 blocks; 552 free (0 chunks); 7640 used
level: 1; TopPortalContext: 8192 total in 1 blocks; 7928 free (2 chunks); 264 used
level: 1; Relcache by OID: 1.048.576 total in 8 blocks; 500672 free (16 chunks); 547904 used
level: 1; CacheMemoryContext: 69.478.096 total in 208 blocks; 44.098.912 free (106056 chunks); 25.379.184 used
level: 2; CachedPlanSource: 4096 total in 3 blocks; 1960 free (1 chunks); 2136 used: <INSERT>
level: 3; unnamed prepared statement: 16384 total in 2 blocks; 6824 free (1 chunks); 9560 used
level: 2; CachedPlan: 8.420.408 total in 15 blocks; 1409824 free (1 chunks); 7010584 used: <SELECT>
level: 2; index info: 2048 total in 2 blocks; 528 free (1 chunks); 1520 used: pg_toast_295195_index
level: 2; CachedPlan: 8192 total in 4 blocks; 2480 free (0 chunks); 5712 used: <DELETE>
level: 2; index info: 2048 total in 2 blocks; 824 free (0 chunks); 1224 used: pg_sequence_seqrelid_index
level: 2; CachedPlan: 2048 total in 2 blocks; 280 free (0 chunks); 1768 used: <OTHER UNIQUE SQL>
level: 2; CachedPlan: 2048 total in 2 blocks; 528 free (0 chunks); 1520 used: <OTHER UNIQUE SQL>
level: 2; CachedPlan: 2048 total in 2 blocks; 16 free (0 chunks); 2032 used: <OTHER UNIQUE SQL>
level: 2; CachedPlan: 2048 total in 2 blocks; 160 free (1 chunks); 1888 used: <OTHER UNIQUE SQL>
level: 2; CachedPlan: 2048 total in 2 blocks; 528 free (0 chunks); 1520 used: <OTHER UNIQUE SQL>
level: 2; index info: 3072 total in 2 blocks; 696 free (1 chunks); 2376 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 824 free (0 chunks); 1224 used: <OTHER UNIQUE INDEX NAME>
level: 2; CachedExpression: 1024 total in 1 blocks; 488 free (0 chunks); 536 used
level: 2; CachedPlan: 2048 total in 2 blocks; 208 free (1 chunks); 1840 used: TO_NUMBER(p_input, p_fmt)
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 856 free (1 chunks); 2216 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 920 free (0 chunks); 1128 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3544 total in 3 blocks; 960 free (1 chunks); 2584 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 4096 total in 3 blocks; 1912 free (3 chunks); 2184 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 840 free (0 chunks); 1208 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 824 free (0 chunks); 1224 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 504 free (0 chunks); 1544 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 856 free (1 chunks); 2216 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1016 free (1 chunks); 2056 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 4024 total in 3 blocks; 816 free (1 chunks); 3208 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 7032 total in 4 blocks; 1928 free (2 chunks); 5104 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 4744 total in 3 blocks; 240 free (0 chunks); 4504 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 7032 total in 4 blocks; 1928 free (2 chunks); 5104 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3304 total in 3 blocks; 784 free (1 chunks); 2520 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1080 free (1 chunks); 1992 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3304 total in 3 blocks; 784 free (1 chunks); 2520 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 904 free (0 chunks); 1144 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 824 free (0 chunks); 1224 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 448 free (1 chunks); 1600 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 8192 total in 4 blocks; 3824 free (2 chunks); 4368 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 544 free (2 chunks); 1504 used: <OTHER UNIQUE INDEX NAME>
level: 2; CachedPlan: 2048 total in 2 blocks; 528 free (0 chunks); 1520 used: v_interval::INTERVAL
level: 2; CachedPlan: 2048 total in 2 blocks; 528 free (0 chunks); 1520 used: (v_interval IS NOT NULL)
level: 2; CachedPlan: 2048 total in 2 blocks; 144 free (1 chunks); 1904 used: v_interval := p_interval_length || ' second'
level: 2; CachedPlan: 2048 total in 2 blocks; 224 free (1 chunks); 1824 used: (p_interval = 'SECOND')
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1096 free (2 chunks); 1976 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1160 free (1 chunks); 1912 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1096 free (2 chunks); 1976 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1160 free (1 chunks); 1912 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1096 free (2 chunks); 1976 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1160 free (1 chunks); 1912 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1096 free (2 chunks); 1976 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1160 free (1 chunks); 1912 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 688 free (1 chunks); 1360 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1016 free (1 chunks); 2056 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1080 free (1 chunks); 1992 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1016 free (1 chunks); 2056 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1080 free (1 chunks); 1992 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1016 free (1 chunks); 2056 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1080 free (1 chunks); 1992 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1016 free (1 chunks); 2056 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1080 free (1 chunks); 1992 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1016 free (1 chunks); 2056 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1080 free (1 chunks); 1992 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 3072 total in 2 blocks; 1016 free (1 chunks); 2056 used: <OTHER UNIQUE INDEX NAME>
level: 2; index info: 2048 total in 2 blocks; 608 free (1 chunks); 1440 used: <OTHER UNIQUE INDEX NAME>
level: 1; 4141 more child contexts containing 12.748.648 total in 8713 blocks; 3.899.520 free (3559 chunks); 8.849.128 used
level: 1; WAL record construction: 49768 total in 2 blocks; 6360 free (0 chunks); 43408 used
level: 1; PrivateRefCount: 8192 total in 1 blocks; 1576 free (0 chunks); 6616 used
level: 1; MdSmgr: 524.288 total in 7 blocks; 412.640 free (8661 chunks); 111648 used
level: 1; LOCALLOCK hash: 1.048.576 total in 8 blocks; 215936 free (27 chunks); 832640 used
level: 1; Timezones: 104120 total in 2 blocks; 2616 free (0 chunks); 101504 used
level: 1; ErrorContext: 8192 total in 1 blocks; 7928 free (4 chunks); 264 used
Grand total: 100.635.144 bytes in 9342 blocks; 53.175.720 free (127010 chunks); 47459424 used
postgresql
Martin Hope
Peter
Asked: 2024-04-08 14:29:14 +0800 CST
  • 5

很明显，在会话上设置synchronous_commit OFF - 其超级罕见的缺点（据称在服务器崩溃的情况下会丢失提交的事务） - 很好，可以提高这些会话的性能，因为它们不必等待 WAL刷新到磁盘。

但是，我无法理解的是这如何影响在同一时间窗口内提交的所有会话synchronous_commit ON。

据我了解，synchronous_commit OFF产生 WAL 的会话与拥有 WAL 的会话一样多ON（甚至更多，因为它们在同一时间完成更多工作，因为它们不必等待 WALWrite）。那么拥有它的会话ON会像所有会话都拥有它一样慢吗ON？

场景 1：10 个执行大量 DML 的会话拥有它ON，10 个会话拥有它OFF。

场景 2：20 个执行大量 DML 的会话ON。

我认为会发生什么：在场景 1 中，10 个会话OFF产生的 WAL 比场景 2 中更多，因此会话ON等待 WALWrite 的时间比场景 1 中更长。

我是否正确理解每次提交总是等待所有当前（xid<=自己的xid）WAL 数据被写入而不仅仅是“它自己的”WAL 数据？

postgresql
Martin Hope
Peter
Asked: 2024-04-04 16:28:36 +0800 CST
  • 5

我们发现提交WALWrite在某些高负载时期过度等待。不仅是某些会话，而且所有提交，甚至真空。通过拍摄快照pg_stat_all_tables，pg_statio_all_tables我认为很明显，在这些WALWrite事件如此突出的特定时期，一张特定的桌子及其吐司桌是罪魁祸首。WALWrite在存在大量等待期间，它会接收大量插入、更新和删除操作。就会话数量（大约 20 个）和数据量（大文本字段）而言，“繁重”。

看看pg_stat_wal等待期间的快照，我可以看到：

  • wal_records每秒从平均 2.000 增加到 10.000-20.000
  • wal_fpi每秒从平均 150 增加到 500-1.000
  • wal_kbytes每秒从平均 600 次增加到 3.000-5.000 次
  • wal_write每秒wal_sync从平均 50 增加到 200

上述数字是否pg_stat_wal表明 WALWrite 事件的原因是什么？

  • 是每秒提交的次数吗？
  • 是提交的大小（以兆字节为单位）吗？
  • 是同时提交的会话数吗？

如果这些数字不能清晰地描绘出情况，我该如何找出答案？我想解决瓶颈，但需要先确定它。

规格更新

  • AWS RDS 上的 PG 14.1 (db.r6i.4xlarge (16 vCPU, 128GB RAM)，带有 1 个副本 (db.r6i.2xlarge)。
  • 存储类型为通用 SSD (gp3)，预配置 IOPS 为 12000 IOPS，存储吞吐量为 500 MiBps。
  • 没有 PostgreSQL 专用日志卷
  • checkpoint_timeout900
  • max_wal_size 15360
  • min_wal_size 8192
  • synchronous_standby_names无效的
  • wal_level复制品
  • wal_buffers64MB
  • shared_buffers32GB
  • wal_compression在
  • commit_delay0
  • synchronous_commit在
postgresql
Martin Hope
Peter
Asked: 2024-03-25 21:38:35 +0800 CST
  • 5

哪些表、索引等在过去 5 分钟或过去 1 小时内获得了 I/O，以及按行读取/秒、行写入/秒字节读取/秒字节写入/秒计算的数量是多少？

这是我希望能够回答的问题。最好甚至知道有多少是从缓冲区提供的，有多少是从磁盘提供的。

有看到这个的景色吗？有什么办法可以查到吗？

postgresql
Martin Hope
Peter
Asked: 2024-03-13 17:06:45 +0800 CST
  • 5

我们的 DB 时区是 UTC。有时，我的用户忘记将其会话时区更改为 UTC，然后他们会出现不需要的行为（例如，在使用时now()）。

有没有办法

  1. 强制所有会话使用 UTC 时区？
  2. 至少在连接时强制它们一次？
  3. 查询所有会话，他们使用什么时区设置？pg_stat_activity似乎不包含该信息。

示例为什么timestamp不能解决我所有的问题：

create table a (c timestamp);
reset timezone;
show timezone; -- UTC
insert into a select now();
select * from a; -- 2024-03-13 12:50:14.515
set timezone to 'UTC+9';
show timezone; -- UTC+9
truncate a;
insert into a select now();
select * from a; -- 2024-03-13 03:50:48.376
reset timezone;
show timezone; -- UTC
select * from a; -- 2024-03-13 03:51:22.854
postgresql
Martin Hope
Peter
Asked: 2024-03-11 17:39:03 +0800 CST
  • 5

通过pg_proctab()，我可以看到我们应用程序的连接在 postgres 中每个连接最多可以使用 800MB 的 RAM。通常最多 400MB。（在评论后进行更新以澄清：这些连接来自连接池，大多数时候它们处于空闲状态，中间有查询。400MB 是在连接空闲时测量的。）

我想调查一下这400MB是由什么组成的。例如，为什么是 400MB，而不仅仅是 40MB？我已经查看了应用程序端的 jdbc 连接对象，没有发现任何异常。

我（疯狂）的猜测是，高 RAM 使用率是因为我们的表上有很多分区。

postgres 是否提供了一种方法来查看连接进程的 RAM？我们使用 AWS RDS，所以最好的情况是我不需要服务器访问的方式。

postgresql