Category Archives: Database

All posts related to databases – design, sql, performance, etc.

View All MySQL Processes

I was recently debugging a long running database query. In most cases MySQL’s Slow Query Log is a great debugging tool for that. However, in this case I found MySQL’s show processlist to be a better fit. What show processlist … Continue reading

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MySQL – WordPress & Avoiding unneeded Group By clauses

A client recently reached out in regard to a reproducible performance problem on their WordPress site.  The use case and conditions were as follows: Performance was fine until a change happened to the wp_posts or wp_term_relationships tables (i.e. when a … Continue reading

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MySQL – inner join vs. exists() may yield better performance

Here’s another example of why it’s always a good idea to refer to execution plans and test different query options.  Here’s a query I was running as part of some manual data work: SELECT ua.* FROM vn_user_achievements ua WHERE EXISTS … Continue reading

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MySQL – Got error 28 from storage engine

Just after a late night deployment I received this error message while running queries against the production database I just deployed to: Got error 28 from storage engine query I could connect to the database fine, but any database query … Continue reading

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PlainCart login problem, and why are they still on MySQL versions < 4.1?

A client shot me an email asking for help w/a PlainCart installation he’s trying to setup. The symptom was that the supposed login credentials of admin, admin weren’t working. Reproducing the problem was simple enough, going to the login page … Continue reading

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MySQL: Index Column Order Matters

I was recently asked about whether column order matters in composite indexes, and if so, to what extent.  I recall this being the case when working with SQL Server 2000 and 2005, so I became curious how MySQL handled scenarios … Continue reading

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Referential Integrity – a fundamental that enables smarter and more cost effective database applications

More often than not, I find the database layer is typically a realm in applications that isn’t emphasized very much. There are certainly developers out there comfortable working with databases, but with the rise of database abstraction layers, query builders, … Continue reading

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