Emergency

Search Results for: mysql convert char to varchar

A recovery trivia or how to recover from a lost ibdata1 file

A few day ago, a customer came to Percona needing to recover data. Basically, while doing a transfer from one SAN to another, something went wrong and they lost the ibdata1 file, where all the …

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Innodb row size limitation

I recently worked on a customer case where at seemingly random times, inserts would fail with Innodb error 139. This is a rather simple problem, but due to it’s nature, it may only affect you …

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Lost innodb tables, xfs and binary grep

Before I start a story about the data recovery case I worked on yesterday, here’s a quick tip – having a database backup does not mean you can restore from it. Always verify your backup …

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Beware of MyISAM Key Cache mutex contention

Today I was working with the client loading data to MyISAM tables at very high rate. Hundreds of millions rows are loaded daily into single MySQL instance with bursts up to 100K of records/sec which …

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Stored Function to generate Sequences

Today a customer asked me to help them to convert their sequence generation process to the stored procedure and even though I have already seen it somewhere I did not find it with two minutes …

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Be careful when joining on CONCAT

The other day I had a case with an awful performance of a rather simple join. It was a join on tb1.vid = CONCAT(‘prefix-‘, tb2.id) with tb1.vid – indexed varchar(100) and tb2.id – int(11) column. …

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MyISAM Scalability and Innodb, Falcon Benchmarks

We many times wrote about InnoDB scalability problems, this time We are faced with one for MyISAM tables. We saw that several times in synthetic benchmarks but never in production, that’s why we did not …

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What exactly is read_rnd_buffer_size

Looking for documentation for read_rnd_buffer_size you would find descriptions such as “The read_rnd_buffer_size is used after a sort, when reading rows in sorted order. If you use many queries with ORDER BY, upping this can …

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Why Index could refuse to work ?

Have you ever seen index which refused to be used even if there is every reason for it to work (from the glance view):

Why on the earth index would not be used you …

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Handling big result sets

Sometime it is needed to handle a lot of rows on client side. Usual way is send query via mysql_query and than handle the result in loop mysql_fetch_array (here I use PHP functions but they …

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