SQL – DBA Notes

Oracle SQL

Throughput, latency, concurrency

The difference between making a good and a bad decisions often comes down to the quality of the pre-defined metrics. If the metric is poor…

Postgres SQL

How Consistent Data Snapshots Obtained from Tuples in PostgreSQL-4

Bulent Soylu October 25, 2021 postgres snapshot tuple

What is a data snapshot? Data pages can physically contain several versions of the same row. But each transaction must see only one (or none)…

Postgres SQL

Row Versions in PostgreSQL-3

Bulent Soylu October 25, 2021 commit nested transaction postgres rollback save point tuple virtual transaction

Tuple header As already mentioned, several versions of each row can be simultaneously available in the database. And we need to somehow distinguish one version…

Postgres SQL

Snapshot Isolation and Multi Version Concurrency Control in PostgreSQL-2

Bulent Soylu October 25, 2021 files forks free space map mvcc relations Snaphot isolation toast tuples visibility map

Relations If you look inside tables and indexes, it turns out that they are organized in a similar way. Both are database objects that contain…

Postgres SQL

Transaction Isolation in Postgres-1

Bulent Soylu October 25, 2021 ACID isolation postgres

Probably, everyone is at least aware of the existence of transactions, has come across the abbreviation ACID, and has heard about isolation levels. But we…