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Showing entries 1 to 10 of 16 6 Older Entries

Displaying posts with tag: gdb (reset)

Using gdb to understand what locks (and when) are really set by InnoDB. Part II.
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In the previous post we checked lock requests while executing INSERT INTO t ... SELECT FROM tt where there is an auto_increment column for which the value is generated in the destination table with default innodb_autoinc_lock_mode=1. Based on it I've reported Bug #76563 that is already verified.

Let's continue to study a special case of the statement mentioned above, INSERT INTO t ... SELECT FROM t, that …

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Using gdb to understand what locks (and when) are really set by InnoDB. Part I.
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There is a story behind this post. To make it short, the detailed study presented here started when I noted old Bug #72748 in "No feedback" status few days ago. I considered this status totally wrong and started a discussion on Facebook about it (yes, this is what I usually do, I discuss handling of MySQL bugs in public).

The technical topic of this discussion (blaming aside) was the way AUTO-INC locks are set by InnoDB with default innodb_autoinc_lock_mode=1. …

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Optimizing MySQL Performance: Choosing the Right Tool for the Job
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Next Wednesday, I will present a webinar about MySQL performance profiling tools that every MySQL DBA should know.

Application performance is a key aspect of ensuring a good experience for your end users. But finding and fixing performance bottlenecks is difficult in the complex systems that define today’s web applications. Having a method and knowing how to use the tools available can significantly reduce the amount of time between problems manifesting and fixes being deployed.

In the webinar, titled “Optimizing MySQL Performance: Choosing the Right Tool for the Job,” we’ll start with the …

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How to obtain all executing queries from a core file
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When investigating core files from crashes, one can quite easily figure out which query crashed, as we've seen.

Sometimes you want to just list all the currently executing statements, this is useful for diagnosing hangs or corruptions.

At least GDB 7 supports python macros, which can help us a lot here.   I use a core file from 5.5.27, also a non-debug build but not …



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Using Aspersa to capture diagnostic data
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I frequently encounter MySQL servers with intermittent problems that don’t happen when I’m watching the server. Gathering good diagnostic data when the problem happens is a must. Aspersa includes two utilities to make this easier.

The first is called ’stalk’. It would be called ‘watch’ but that’s already a name of a standard Unix utility. It simply watches for a condition to happen and fires off the second utility.

This second utility does most of the work. It is called ‘collect’ and by default, it gathers stats on a number of things for 30 seconds. It …

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A growing trend: InnoDB mutex contention
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I’ve been noticing an undeniable trend in my consulting engagements in the last year or so, and when I vocalized this today, heads nodded all around me. Everyone sees a growth in the number of cases where otherwise well-optimized systems are artificially limited by InnoDB contention problems.

A year ago, I simply wasn’t seeing the need for analysis of GDB backtraces en masse. These days, I’m writing custom tools to gather and analyze backtraces. A year ago, I simply looked at the SEMAPHORE section of SHOW INNODB STATUS. These days I’m writing custom tools to aggregate and reformat that data so I can interpret it more easily. And I’m …

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Read ahead…
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Mark wrote about how to find situations where InnoDB read-ahead is a bottleneck. What he didn’t disclose, though, is his trick to disable read-ahead without restart or recompile of MySQL. See, there’s no internal “disable read ahead knob”. But there is…

buf_read_ahead_random(...){ ...
       if (srv_startup_is_before_trx_rollback_phase) {
                /* No read-ahead to avoid thread deadlocks */
                return(0);
        }

This variable is tested at two functions – buf_read_ahead_linear() and buf_read_ahead_random() and nowhere …

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GDB 7!
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I wasn’t prepared for this. After spending months playing with GDB development trees I somehow entirely missed that 7.0 release is getting close, and took me more than an hour to spot it.

My favorite features are python scripting and non-stop debugging. I was toying around with python scripting for a while, and was planning to make backtraces make sense. Having hands that open means that one can see PHP backtraces, when gdb’ing apache, see table names and states when MySQL thread access handler interfaces, or remote IPs and users, when it is writing to network. Process inspection can simply rock, if …

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How GDB helped me fix a Drizzle Bug
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The other day I found a nice surprise on my inbox. Jay Pipes asked me if I'd like to try fixing a small bug on Drizzle. It looked pretty simple, and the bug report included a big part of the fix. I accepted without a doubt.
I decided to first change trans_prealloc_size from uint32_t to uint64_t. That was done on

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A script snippet for aggregating GDB backtraces
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A short time ago in a galaxy nearby, Domas Mituzas wrote about contention profiling with GDB stack traces. Mark Callaghan found the technique useful, and contributed an awk script (in the comments) to aggregate stack traces and identify which things are blocking most threads. I’ve used it myself a time or five. But I’ve found myself wanting it to be fancier, for various reasons. So I wrote a little utility that can aggregate and pretty-print backtraces. It can …

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Showing entries 1 to 10 of 16 6 Older Entries

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