Column-Oriented Storage Basic idea: Although fact tables are often over 100 columns wide, a typical data warehouse query only accesses 4 or 5 of them at one time (SELECT *​ queries are rarely needed for analytics) The idea behind column-oriented storage is simple: don’t store all the values from one row together, but store all the values from each column together instead. If each column...

Airwallex调研 2025-02-24 简介 Airwallex（空中云汇）是一家全球领先的金融科技公司，专注于为企业提供跨境支付、外汇兑换、资金管理等一站式...

github ssh 失败 ssh 失败 github 可能会屏蔽 22 的 ssh 端口，导致使用 ssh 协议拉取推送代码失败 解决方法为使用 443 端口，同时将 hostname 改为 ssh.github.com​ host github.com Hostname ssh.github.com...

0x01-8级锁的不对称性 2024-08-17 00:14:26 +0800 用于创建索引的 SHARE LOCK，虽然和修改时需要的 ROW EXCL 锁冲突，却不和自己冲突。虽然创建索引时不能插入数据，但是可以创建其他索引。 SHARE 这个名字非常贴切。 注意：create index 可以事务块中执行 test=# begin transaction; BEGIN test=*# insert into test values (1); INSERT 0 1 test=*# create index on test (a); CREATE INDEX test=*# commit; COMMIT 而为了不阻塞读写，持有 SHARE UPDATE EXCL 锁的行为， 例如 vacuum , create index concurrent ，大都不能在事务块中进行。原因可能是这些操作需要感知其他正在执行的事务的状态(status of running processes)，其行为超出了一般意义上 MVCC 的。

c - What does -fwrapv do? - Stack Overflow -fwrapv tells the compiler that overflow of signed integer arithmetic must be treated as well-defined behavior, even though it is undefined in the C standard. It has two meaning full results: INT_MAX + 1 is overflowed to INT_MIN correctly. This is almost the default behavior in gcc. Don’t let the compiler assume x + 1 > x. See the program below...