Infrastructure at your Service
By Franck Pachot . For an Oracle DBA, we are used to join active sessions (from V$SESSION where status=’ACTIVE) with active statements (from V$SQL where users_executing>0) on the SQL_ID. V$ACTIVE_SESSION_HISTORY also displays the TOP_LEVEL_SQL_ID to get the entrypoint of the usercall if we need it. With Postgres it is a bit more difficult because it seems that PG_STAT_ACTIVITY do not show the active statement but only the top-level one. But pg_stat_statement collects statistics for the…
By Franck Pachot . If you follow this blog, you should know how I like Orachrome Lighty for Oracle, for its efficiency to monitor database performance statistics. Today Orachrome released the beta version of Lighty for Postgres: https://orachrome.com/news/la-beta-de-lighty-for-postgresql-est-ouverte/ The Cloud is perfect to do short tests with more resources than my laptop, especially the predictability of performance, then I started a Bitnami Postgres Compute service on the Oracle Cloud and did some tests with pgbench…
By Franck Pachot . In the Oracle Cloud PaaS you have a marketplace where you can choose your service. Some are packaged from Bitnami and available on multiple OS. My first idea is that in PaaS you do not care about the OS. But Oracle Cloud has this very nice feature where you still have full access to the OS, as root, even in PaaS. Then, you choose the Linux distribution of your preference. Except…
By Franck Pachot . That’s a long blog post title, which is actually just a good pretext to play with Kevin Closson SLOB method for PostgreSQL: pgio I use the beta version of pgio here. If you want to read more about it, you can start on https://kevinclosson.net/2018/05/22/sneak-preview-of-pgio-the-slob-method-for-postgressql-part-i-the-beta-pgio-readme-file/. If you are used to the SLOB for Oracle (https://kevinclosson.net/slob/) you will quickly understand the ‘why’ and ‘how’ of pgio.
Although PostgreSQL 10 integrate native logical replication (have a look here or here), it is always interesting to be aware of alternative solutions to the available in-core features. One of those is called pglogical. It’s a Postgres extension developed by 2ndQuadrant, major contributor to PostgreSQL development. The goal of this blog post is to discover how to install pglogical and configure it in order to generate simple logical replication cases. Installation To get the extension…
By Franck Pachot . In my opinion, the volume of logging (aka redo log, aka xlog, aka WAL) is the most important factor for OLTP performance, availability and scalability, for several reasons: This is the only structure where disk latency is a mandatory component of response time This is a big part of the total volume of backups This is sequential by nature, and very difficult to scale by parallelizing In this post, I look…
By Franck Pachot . Every database analysis should start with system load analysis. If the host is in CPU starvation, then looking at other statistics can be pointless. With ‘top’ on Linux, or equivalent such as process explorer on Windows, you see the process (and threads). If the name of the process is meaningful, you already have a clue about the active sessions. Postgres goes further by showing the operation (which SQL command), the state…
By Franck Pachot . I was going to end this series with the previous post because the last access path available in Postgres is a bit special: a Seq Scan that returns only a sample of the rows, at random. However, it is the occasion to come back to the difference between random and sequential reads.
By Franck Pachot . In the previous post we have seen the cheapest way to get one row, reading only one block from its physical location. But that’s the optimal case where the row has not moved. I’ll (nearly) conclude this series about access path with an update.
By Franck Pachot . In the previous post we have seen how Postgres and Oracle finds the table row from the index entry. It uses the TID / ROWID. I’ll focus on this access path and I will have covered all Postgres access paths to table data. Oracle ACCESS BY ROWID I start with Oracle because we already have seen the TABLE ACCESS BY ROWID. I’ll decompose an index acces to the table. The first…
