PostgreSQL 清理死亡元祖 dead tuples 详解 1.Dead tuples 在Postgresql做delete操作时,数据集(也叫做元组 (tuples))是没有立即从数据文件中移除的,仅仅是通过在行头部设置xmax做一个删除标记。update操作也是一样的,在postgresql中可以看作是先delete再insert; 这是Postgresql MVCC的基本思想之一,因为它允许在不同进...
当你的Java应用程序对 PostgreSQL数据库执行DELETE或UPDATE语句时,不会立即删除已删除的记录,也不会在其位置更新现有记录。相反,删除的记录被标记为Dead Tuples并将保留在存储中。更新的记录实际上是PostgreSQL通过复制先前版本的记录并更新请求的列来插入的全新记录。该更新记录的先前版本被视为已删除,并且与DELETE操作...
如果这种情况发生后,PG就没有办法按transactionID来区分事务的先后,也没有办法实现MVCC了。 因此PG用vacuum后台进程,按一定的周期和算法触发vacuum动作,将过老的tuple的header中的事务ID进行冻结。冻结事务ID,即将事务ID设置为“2”(“0”表示无效事务ID;“1”表示bootstrap, 即初始化;“3”表示最小的事务ID)。PG...
Something that lead to my confusion above is pg_stat_progress_vacuum, each time autovacuum/manual vacuum launch during long running transaction, it reports that num_dead_tuples is 0, while the pg_stat_user_tables.n_dead_tuple still have the number of dead tuples. It is false reporting fr...
Where: while updating tuple (100,26) in relation "realm_attribute"] [update REALM_ATTRIBUTE set VALUE=? where NAME=? and REALM_ID=?] at org.hibernate.dialect.PostgreSQLDialect.lambda$buildSQLExceptionConversionDelegate$1(PostgreSQLDialect.java:944) at org.hibernate.exception.internal.Standard...
VACUUMcan only remove those row versions (also known as “tuples”) that are not needed any more. A tuple is not needed if the transaction ID of the deleting transaction (as stored in thexmaxsystem column) is older than the oldest transaction still active in the PostgreSQL database (or ...
reproducible. This has an incredible amount of value in the long-run. > It's not like somebody else had a great suggestion for how to do this in a > better way either. Sawada-san and John are the two ones in the best position to answer ...
> RECENTLY_DEAD) tuples in the first place, because we don't have to > (pruning removes them instead). It doesn't matter if they're DEAD due > to being from aborted transactions or DEAD due to being > deleted/updated by a transaction that committed (committed and < ...
$ psql --no-psqlrc --tuples-only -c 'select version()' PostgreSQL 14.5 on x86_64-pc-linux-musl, compiled by gcc (Alpine 11.2.1_git20220219) 11.2.1 20220219, 64-bit pgx: $ grep 'github.com/jackc/pgx/v[0-9]' go.mod github.com/jackc/pgx/v5 v5.0.0 Additional context I beli...
[1]:https://www.postgresql.org/docs/9.1/static/runtime-config-locks.html [2]:Postgres sourcexwaitis the transaction that is also attempting to insert the same value. It’s not obvious to me why Postgres implements unique indices in this way. One could imagine an implementation that let bo...