The PostgreSQL Project is present with a booth at FOSDEM ever since 2007. Since 2008 we organize a Devroom, since 2013 we have our own PGDay on the Friday before FOSDEM. This year marks the 8th FOSDEM PGDay.
This blog post presents useful information about the PGDay, the booth and Devroom at FOSDEM.
Continue reading "PostgreSQL @ FOSDEM 2020"
For the 13th year, the PostgreSQL Project is participating in Google Summer of Code (GSoC). This project is a great opportunity to let students learn about Open Source projects, and help them deliver new features. It is also a chance to engage the students beyond just one summer, and grow them into active contributors.
In GSoC, students first learn about the Open Source organization, and either pick a summer project from the list provided by the org, or submit their own idea for review. After a “community bonding” period, the students have time to implement their idea, under supervision of mentors from the Open Source organization. There is also an incentive: first, Google pays the students for their work on improving Open Source projects. And second, having a completed GSoC project in a CV is well recognized.
Continue reading "Google Summer of Code 2019 - PostgreSQL participates with 5 projects"
At FOSDEM someone asked how long 64 bit Transaction-IDs will last.
To refresh: PostgreSQL is currently using 32 bits for the TXID, and is good for around 4 billion transactions:
fosdem=# SELECT 2^32;
That will not last very long if you have a busy database, doing many writes over the day. MVCC keeps the new and old versions of a row in the table, and the TXID will increase with every transaction. At some point the 4 billion transactions are reached, the TXID will overrun, and start again at the beginning. The way transactions are working in PostgreSQL, suddenly all data in your database will become invisible. No one wants that!
To limit this problem, PostgreSQL has a number mechanism in place:
- PostgreSQL splits transaction ids into half: 2 billion in the past are visible, 2 billion in the future are not visible - all visible rows must live in the 2 billion in the past, at all times.
- Old, deleted row versions are enevtually removed by VACUUM (or Autovacuum), the XID is no longer used.
- Old row versions, which are still live, are marked as "freezed" in a table, and assigned a special XID - the previously used XID is no longer needed. The problem here is that every single table in every database must be Vacuumed before the 2 billion threshold is reached.
- PostgreSQL uses lazy XIDs, where a "real" transaction id is only assigned if the transaction changes something on disk - if a transaction is read only, and does not change anything, no transaction id is consumed.
Continue reading "How long will a 64 bit Transaction-ID last in PostgreSQL?"