Month: August 2016

There’s new evidence that standing desks in classrooms can slow the increase in elementary school children’s body mass index (BMI)—a key indicator of obesity—by an average of 5.24 percentile points.

“Research around the world has shown that standing desks are positive for the teachers in terms of classroom management and student engagement, as well as positive for the children for their health, cognitive functioning and academic achievement,” says Mark Benden, an associate professor in environmental and occupational health at the Texas A&M School of Public Health and an author of the study published in the American Journal of Public Health.

“It’s literally a win-win, and now we have hard data that shows it is beneficial for weight control.”

Same results for boys and girls

Twenty-four classrooms at three elementary schools (eight in each of the three schools) in College Station, Texas, participated in the study. At each school, four classrooms were outfitted with stand-biased desks (which allow students to sit on a stool or stand at will) and four classrooms in each school acted as a control and utilized standard classroom desks.

The researchers followed the same students—193 in all—from the beginning of third grade to the end of fourth grade.

The researchers found that the students who had the stand-biased desks for both years averaged a three percent drop in BMI while those in traditional desks showed the two percent increase typically associated with getting older. However, even those who spent just one year in classrooms with stand-biased desks had lower mean BMIs than those students in traditional seated classrooms for their third and fourth grade years.

If you give kids too much food, they’ll overeat

In addition, there weren’t major differences between boys and girls, or between students of different races, suggesting that this intervention works across demographic groups.

“Classrooms with stand-biased desks are part of what we call an Activity Permissive Learning Environment (APLE), which means that teachers don’t tell children to ‘sit down,’ or ‘sit still’ during class,” Benden says. “Instead, these types of desks encourage the students to move instead of being forced to sit in poorly fitting, hard plastic chairs for six or seven hours of their day.”

Range of starting weights

Previous studies from Benden’s lab have shown that children who stand burn 15 percent more calories, on average, than those who sit in class, but this is the first study showing, over two years, that BMI decreases over time (versus controls) when using a stand-biased desk.

“It is challenging to just measure weight loss with children,” Benden says, “because children are supposed to be gaining weight as they get older and taller.”

At the beginning of this study, roughly 79 percent of the students were of normal weight category, 12 percent were overweight, and nine percent were obese, according to height and weight measurements made by the researchers. These are better numbers than nationally, where 14.9 percent of children were overweight and 16.9 percent were obese in 2012.

The fact that the students who started at a healthy weight benefited from stand-biased desks as much as they did might indicate that these desks help students who aren’t overweight maintain their BMI, while at the same time help those who start out overweight or obese get to a healthier weight.

The desks, designed by Benden and his team, are called stand-biased, not “standing” because they do include a tall stool the students can perch on if they so choose. They also include a footrest, a vital feature because it allows children to get their lower backs out of tension and reduce leg fatigue to stand more comfortably over time. These United States-patented desk designs are now licensed to Stand2Learn, which has commercialized the products through translational research focused on moving university studies to publicly available solutions.

“Sit less, move more,” Benden says. “That’s our message.”

The National Institutes of Health funded the study.

Source: Texas A&M University

The post Standing desks in schools linked to lower BMIs appeared first on Futurity.

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Thank you for attending my 22nd July 2016 webinar titled “Top Most Overlooked MySQL Performance Optimizations“. In this blog, I will provide answers to the Q & A for that webinar.

For hardware, which disk raid level do you suggest? Is raid5 suggested performance-wise and data-integrity-wise?
RAID 5 comes with high overhead, as each write turns into a sequence of four physical I/O operations, two reads and two writes. We know that RAID 5s have some write penalty, and it could affect the performance on spindle disks. In most cases, we advise using alternative RAID levels. Use RAID 5 when disk capacity is more important than performance (e.g., archive databases that aren’t used often). Since write performance isn’t a problem in the case of SSD, but capacity is expensive, RAID 5 can help by wasting less disk space.

Regarding collecting table statistics, do you have any suggestions for analyzing large tables (over 300GB) since we had issues with MySQL detecting the wrong cardinality?
MySQL optimizer makes decisions about the execution plan (EXPLAIN), and statistics are re-estimated automatically and can be re-estimated explicitly when one calls the ANALYZE TABLE statement for the table, or the OPTIMIZE TABLE statement for InnoDB tables (which rebuilds the table and then performs an ANALYZE for the table).

When MySQL optimizer is not picking up the right index in EXPLAIN, it could be caused by outdated or wrong statistics (optimizer bugs aside). So, when you optimize the table you rebuild it so data are stored in a more compact way (assuming they changed a lot in the past) and then you re-estimate statistics based on some random sample pages checked in the table. As a result, you come up with statistics that are more correct for the data you have at the moment. This allows optimizer to get a better plan. When an explicit hint is added, you reduce possible choices for optimizer and it can use a good enough plan even with wrong statistics.

If you use versions 5.6.x and 5.7.x, and InnoDB tables, there is a way to store/fix statistics when the plans are good.  Using Persistent Optimizer Statistics prevents it from changing automatically. It’s recommended you run ANALYZE TABLE to calculate statistics (if really needed) during off peak time and make sure the table in question is not in use. Check this blogpost too.

Regarding the buffer pool, when due you think using multiple buffer pool instances make sense?
Multiple InnoDB buffer pools were introduced in MySQL 5.5, and the default value for it was 1. Now, the default value in MySQL 5.6 is 8. Enabling

innodb_buffer_pool_instances

 is useful in highly concurrent workloads as it may reduce contention of the global mutexes.

innodb_buffer_pool_instances

 helps to improve scalability in multi-core machines and having multiple buffer pools means that access to the buffer pool splits across all instances. Therefore, no single mutex controls the access pattern.

innodb_buffer_pool_instances

 only takes effect when set to 1GB (at minimum), and the total specified size for

innodb_buffer_pool

  is divided among all the buffer pool instances. Further, setting the innodb_buffer_pool_instances parameter is not a dynamic option, so it requires a server restart to take effect.

What do you mean “PK is appended to secondary index”
In InnoDB, secondary indexes are stored along with their corresponding primary key values. InnoDB uses this primary key value to search for the row in the clustered index. So, primary keys are implicitly added with secondary keys.

About Duplicate Keys, if I have a UNIQUE KEY on two columns, is it ok then to set a key for each of these columns also? Or should I only keep the unique key on the columns and get rid of regular key on each column also?
As I mentioned during the talk, for composite index the leftmost prefix is used. For example, If you have a UNIQUE INDEX on columns A,B as (A,B), then this index is not used for lookup for the query below:

SELECT * FROM test WHERE B='xxx';

For that query, you need a separate index on B column.

On myisam settings, doesn’t the MySQL and information_schema schemas require myisam? If so, are any settings more than default needing to be changed?
performance_schema uses the PERFORMANCE_SCHEMA storage engine, so only MySQL system database tables use the MyISAM engine. The MySQL system database is not used much and usually default settings for MyISAM engine are fine.

Will functions make my app slow compare than query?
I’m not sure how you’re comparing “queries” versus “stored functions.” Functions also need to transform, similar to the query execution plan. But it might be slower compare to well-coded SQL, even with the overhead of copying the resulting data set back to the client. Typically, functions have many SQL queries. The trade-off is that this does increase the load on the database server because more of the work is done on the server side and less is done on the client (application) side.

Foreign key will make my fetches slower?
MySQL enforces referential integrity (which ensures data consistency between related tables) via foreign keys for the InnoDB storage engine. There could be some overhead of this for the INSERT/UPDATE/DELETE foreign key column, which has to check if the value exists in a related column of other tables. There could be some overhead for this, but again it’s an index lookup so the cost shouldn’t be high. However, locking overhead comes into play as well. This blogpost from our CEO is informative on this topic. This especially affect writes, but I don’t think FK fetches slower for SELECT as it’s an index lookup.

Large pool size can have a negative impact to performance? About 62GB of pool size?
The InnoDB buffer pool is by far the most important option for InnoDB Performance, as it’s the main cache for data and indexes and it must be set correctly. Setting it large enough (i.e., larger than your dataset) shouldn’t cause any problems as long as you leave enough memory for OS needs and for MySQL buffers (e.g., sort buffer, join buffer, temporary tables, etc.).

62GB doesn’t necessarily mean a big InnoDB buffer pool. It depends on how much memory your MySQL server contains, and what the size of your total InnoDB dataset is. A good rule of thumb is to set the InnoDB buffer pool size as large as possible, while still leaving enough memory for MySQL buffers and for OS.

You find duplicate, redundant indexes by looking at information_schema.key_column_usage directly?
The key_column_usage view provides information about key columns constraints. It doesn’t provide information about duplicate or redundant indexes.

Can you find candidate missing indexes by looking at the slow query log?
Yes, as I mentioned you can find unused indexes by enabling log_queries_not_using_indexes. It writes to

slow_query_log

. You can also enable the user_statistics feature which adds several information_schema tables, and you can find un-used indexes with the help of user_statistics. pt-index-usage is yet another tool from Percona toolkit for this purpose. Also, check this blogpost on this topic.

How to find the unused indexes? They also have an impact on performance.
Unused indexes can be found with the help of the pt-index-usage tool from Percona toolkit as mentioned above. If you are using Percona Server, you can also use User Statistics feature. Check this blogpost from my colleague, which shows another technique to find unused indexes.

As far as I understand, MIXED will automatically use ROW for non-deterministic and STATEMENT for deterministic queries. I’ve been using it for years now without any problems. So why this recommendation of ROW?

In Mixed Mode, MySQL uses statement-based replication for most queries, switching to row-based replication only when statement-based replication would cause an inconsistency. We recommend ROW-based logging because it’s efficient and performs better as it requires less row locks. However, RBR can generate more data if a DML query affects many rows and a significant amount of data needs to be written to the binary log (and you can configure

binlog_row_image

 parameter to control the amount of logging). Also, make sure you have good network bandwidth between master/slave(s) for RBR, as it needs to send more data to slaves. Another important thing to get best of the performance with ROW-based replication is to make sure all your database tables contain a Primary Key or Unique Key (because of this bug http://ift.tt/XAfSeJ?id=53375).

Can you give a brief overview of sharding…The pros and cons also.
With Sharding, database data is split into multiple databases with each shard storing a subset of data. Sharding is useful to scale writes if you have huge dataset and a single server can’t handle amount of writes.

Performance and throughput could be better with sharding. On the other had, it requires lots of development and administration efforts. The application needs to be aware of the shards and keep track of which data is stored in which shard. You can use MySQL Fabric framework to manage farms of MySQL Servers. Check for details in the manual.

Why not mixed replication mode instead of row-based replication ?
As I mentioned above, MIXED uses a STATEMENT-based format by default, and converts to ROW-based replication format for non-deterministic queries. But ROW-based format is recommended as there could still be cases where MySQL fails to detect non-deterministic query behavior and replicates in a STATEMENT-based format.

Can you specify a few variables which could reduce slave lag?
Because of the single-threaded nature of MySQL (until MySQL 5.6), there is always a chance that a MySQL slave can lag from the master. I would suggest considering the below parameters to avoid slave lag:

• innodb_flush_log_at_trx_commit <> 1, Either set it t or 0 however, it could cause you 1 second of data loss in case of crash.
• innodb_flush_method = O_DIRECT, for unix like operating system O_DIRECT is recommended to avoid double buffering. If your InnoDB data and log files are located on SAN then O_DIRECT is probably not good choice.
• log_bin = 0, Disable binary logging (if enabled) to minimize extra Disk IO.
• sync_binlog = 0, Disable sync_binlog.

Those above parameters would definitely help to minimize slave lag. However, along with that make sure your slave(s) hardware is as strong as the master. Make sure your read queries are fast enough. Don’t overload slave to much, and distribute read traffic evenly between slave(s). Also, you should have the same table definitions on slave(s) as the master (e.g., master server indexes must exists on slave(s) tables too). Last but not least, I wrote a blogpost on how to diagnose and cure replication lag. It might be useful for further reading.

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During the medals ceremony for the 200 meter race the 1968 Olympics, gold medalist Tommie Smith and bronze medalist John Carlos, both standing shoeless on the podium, each raised one black-gloved fist in the air during the playing of the US national anthem as a gesture in support of the fight of better treatment of African Americans in the US. It was an historic moment immortalized in photos like the one above.

The white man in the photo, silver medalist Peter Norman from Australia, could be considered a sort of symbolic visual foil against which Smith and Carlos were protesting, but in fact Norman was a willing participant in the gesture and suffered the consequences.

Norman was a white man from Australia, a country that had strict apartheid laws, almost as strict as South Africa. There was tension and protests in the streets of Australia following heavy restrictions on non-white immigration and discriminatory laws against aboriginal people, some of which consisted of forced adoptions of native children to white families.

The two Americans had asked Norman if he believed in human rights. Norman said he did. They asked him if he believed in God, and he, who had been in the Salvation Army, said he believed strongly in God. "We knew that what we were going to do was far greater than any athletic feat, and he said "I’ll stand with you" — remembers John Carlos — "I expected to see fear in Norman’s eyes, but instead we saw love."

Tags: 1968 Summer Olympics   John Carlos   Olympic Games   Peter Norman   photography   racism   Tommie Smith
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The white man in the photo of the Black Power salute at the 1968 Olympics)

Stormtroopers may seem like faceless, disposable soldiers that the Empire uses for blaster fodder, and they are from a certain point of view, but they are also people, with a life, as well as hopes and dreams. This short film shows the human side of Stormtroopers and shows you the life of one.

TK-436: A Stormtrooper Story is an amazing short that was produced by Samtubia & Samgoma Edwards. After watching it, you will see why it won the Filmmaker’s Choice award at this year’s Star Wars Celebration Europe event. In the story, a Stormtrooper is forced to confront his past in the middle of an epic battle. It is a sad tale, very reminiscent of some Civil War stories.

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TK-436: A Stormtrooper Story

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The respite, peace, and sense of solitude that we get from exploring and playing No Man’s Sky is a t