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Showing entries 1 to 10 of 27 10 Older Entries

Displaying posts with tag: memory (reset)

volatile considered harmful
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While playing with MySQL 5.7.5 on POWER8, I came across a rather interesting bug (74775 - and this is not the only one… I think I have a decent amount of auditing and patching to do now) which made me want to write a bit on memory barriers and the volatile keyword.

Memory barriers are hard.

Like, super hard. It’s the kind of thing that makes you curse hardware designers, probably because they’re not magically solving all your problems for you. Basically, as you get more CPU cores and each of them have caches, it gets more expensive to keep everything in sync. …

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Active-Active Replication, Performance Improvements & Operational Enhancements – some of what’s available in the new MySQL Cluster 7.4.2 DMR
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Oracle have just made availble the new MySQL Cluster 7.4.2 Development Milestone Release – it can be downloaded from the development release tab here. Note that this is not a GA release and so we wouldn’t recommend using it in production.

This is the second DMR for MySQL 7.4; the delta between this DMR and 7.4.1 can be viewed in the …

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OOM relation to vm.swappiness=0 in new kernel
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I have recently been involved in diagnosing the reasons behind OOM invocation that would kill the MySQL server process. Of course these servers were primarily running MySQL. As such the MySQL server process was the one with the largest amount of memory allocated.

But the strange thing was that in all the cases, there was no swapping activity seen and there were enough pages in the page cache. Ironically all of these servers were CentOS 6.4 running kernel version 2.6.32-358. Another commonality was the fact that vm.swappiness was set to 0. This is a pretty much standard practice and one that is applied on nearly every server that runs …

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on swapping and kernels
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There is much more to write about all the work we do at Facebook with memory management efficiency on our systems, but there was this one detour investigation in the middle of 2012 that I had to revisit recently courtesy of Wikipedia.

There are lots of factors that make machines page out memory segments into disk, thus slowing everything down and locking software up – from file system cache pressure to runaway memory leaks to kernel drivers being greedy. But certain swap-out scenarios are confusing – systems seem to have lots of memory available, with proper settings file system cache should not cause swapping, and obviously in production environment all the memory …

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Memory Leak (and Growth) Flame Graphs
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Memory Leak

Memory Flame Graph    

Your application memory usage is steadily growing, and you are racing against time to fix it. This could either be memory growth due to a misconfig, or a memory leak due to a software bug. For some applications, performance can begin to degrade as garbage collection works harder, consuming CPU. If an application grows too large, performance can drop off a cliff due to paging (swapping), or the application may …

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The MEMORY storage engine
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I recently wrote about Where are they now: MySQL Storage Engines and The MERGE storage engine: not dead, just resting…. or forgotten. Today, it’s the turn of the MEMORY storage engine – otherwise known as HEAP.

This is yet another piece of the MySQL server that sits largely unmaintained and unloved. The …

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Tab Sweep: Email, AntClassLoader, CouchBase Manager, Memory Usage, ...
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Recent Tips and News on Java, Java EE 6, GlassFish & more :

Java, GlassFish v3, High CPU and Memory Usage, Locked Threads, Death (Gregor Bowie)
Why I will continue to use Spring *and* Java EE in new …

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MySQL, OOM Killer, and everything related
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Do the operating systems kill your MySQL instances from time to time? Are some database servers swapping constantly? These are relatively common problems. Why? How to prevent them?

Memory allocation

When a running program needs some additional memory, it can typically allocate it dynamically with malloc() function. It finds an unused continuous block that is at least as large as the requested size, reserves as much as it needs, and returns a pointer to that space. No initialization of the memory contents is performed at the time. When malloc() returns NULL instead of a valid address, it is an information to the …

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An elaborate way to break a MySQL server with XtraBackup
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XtraBackup is a great piece of software from Percona, which allows creating (nearly) lock-less MySQL/InnoDB backups. The tool has been around for quite some time and recently even received a major version bump. I have relied on it many times over the years. As it turns out, using it in some configurations may lead to heavy swapping or prevent MySQL from running queries.

So far I only kept complaining about the wrapper script XtraBackup has been distributed with and which was taken from Oracle’s InnoDB Hot Backup. The infamous innobackupex-1.5.1 was neither well written, nor was it even fully compatible with the …

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How having many tables affects MySQL memory usage?
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You could say: what could be the reason for having really big number of tables? Just design the application properly! It’s not always that easy. And this post isn’t really about arguing whether having many tables is good or not, it’s about what happens in terms of memory usage if you already reached that point.

Btw what do I mean by *many*? From my experience it’s tens of thousends or even millions rather than hundreds.

The inspiration for me to write this post was strong desire to try out the latest declared …

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Showing entries 1 to 10 of 27 10 Older Entries

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