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What to Change On Your Bike If Your Hands or Legs Go Numb When Riding

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When MySQL optimizer is not picking up the right index in EXPLAIN, it could be caused by outdated or wrong statistics (optimizer bugs aside).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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Top Most Overlooked MySQL Performance Optimizations: Q & A

Sequences are objects defined by the SQL standard that are used to create monotonically increasing sequences of numeric values. Whenever nextval is called on a sequence object, it generates and returns the next number in the sequence. For MySQL and MariaDB users, this might sound similar to MySQL’s AUTO_INCREMENT columns, but there are some differences: Sequences are defined by the … Read More
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Emulating Sequences in MySQL and MariaDB

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.

via MightyMega
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

The graphite-barreled MLR22AT rifle I tested about a year before I wrote this review was about half the price of the rifles I tested in my Ultimate 10/22 shootout. It was not only nipping at the heels of high-dollar competition 10/22s, but full on leg-biting competition brands like Kidd and Volquartsen from a performance perspective.

The Magnum Research 10/22 clone rifles are kinda like the guy in the tweaked Nissan 300Z who can keep up and occasionally beat the guys in million-dollar sports cars. These guns offer a lot at a $599+optic MSRP instead of $1000+optic MSRP.

Magnum Research now also offers the MLR22ATU, which has the same specs as the original model but with a lightweight, tensioned 18” aluminum-sleeved barrel instead of the graphite barrel.

For the price, the Magnum Research MLR-22 line is one hell of a head-turner on the bench and downrange when inspecting the tiny groups. The same buddy who had previously shared a similar comment on the graphite model again asked “why would I buy anything else when this is under $600?” The Magnum Research line is a phenomenal deal when it comes to performance and all the extras included.

My rifle included a stock Magnum Research MLR22ATU rifle which comes with CNC billet upper receiver, billet machined match bolt, custom charging handle, lightweight stock, proprietary aluminum-sleeved tensioned barrel with Benz target chamber, and the remainder of the parts are mostly stock Ruger spec.

For testing, I added a $420 Lucid 4x-16xx44mm Crossover scope, which allowed me to make accurate shots out to 200 yards, making it well worth the price to me.

Fit, Finish, Feel, and Features

The MLR22AT with 16” graphite barrel and this MLR22ATU with 18″ aluminum sleeve barrel feature roughly the same components with the exception of the barrels. I was impressed with the capabilities of this rifle considering its price and weight, even with the stock Ruger trigger assembly. The rifle is amazingly lightweight, and the 18″ barrel is only about a quarter-pound heavier than the graphite model.

The MLR22ATU is by far one of the lightest production 10/22 rifles made, at an insanely light 4.5 pounds. It’s also a bit showier than the graphite model due to the beautiful aluminum-sleeved barrel. The billet machined receiver is every bit as nice as the custom receivers I have tested.

The trigger is a stock Ruger 10/22 unit, which means it is far from a premium match trigger, but the “new version” Ruger 10/22 stock trigger is “not bad.” Even in stock form, this rig can get shooters consistently into the high .1xx” and low .2xx” sized groups out to 50 yards with a clear optic.

Magnum Research upgraded to a stock Ruger extended magazine release from the earlier model I tested and also added a pair of sling studs. I also noticed that they now include turned and hardened receiver pins instead of stock Ruger pins. A threaded barrel option is available for a $40 upcharge.

The bolt is not showy, but is an in-house machined part with extra tuning features such as pinned firing pin and correctly-dimensioned face. It is a well-finished part, but it does not include the extra little decorative cuts like you see on some other custom 10/22 bolts.

The charging handle is big, but perfect for a working man’s rifle; I love it. You can even work the bolt with big heavy mittens in the bitter cold — or in my case while wearing welding gloves in the garage.

The stock is light and sturdy and an excellent interpretation of a Boyd’s Evolution stock, but far lighter. Because of that light weight, I like it better on this rifle although it is designed around a shorter length of pull.

The Magnum Research MLR22AT packs a lot of great components an affordable, ready-to-go rifle. This is an efficient build that puts the upgrades where they matter.

Accuracy

I am fortunate that I can test both the graphite and tensioned barreled models side by side. The graphite model has the edge on accuracy, but not by much. It may be that my older MLR22AT just has a more worn-in trigger, but I consistently see groups several hundredths of an inch smaller with the older graphite barrel. Of course, when you are talking hundredths of an inch it could just be an difference in ammo preference or optic clarity.

Like the older model, this one prefers CCI Standard Velocity, but I also found that the aluminum sleeved version seemed to be more consistent with a variety of ammo than the older graphite barrel.

The barrel is not just an aluminum sleeve over a stainless steel barrel; it is a tensioned stainless barrel. Tensioned barrels basically apply tension at each end of the barrel “stretch it,” to increase barrel strength, reduce harmonics, and increase accuracy. In theory, the tensioned barrel will deliver better accuracy while the aluminum sleeve helps dissipate heat.

This barrel is pre-tensioned and non-adjustable, so you cannot “tune” the barrel yourself.

Magnum Research again used a 22LR Benz match chamber for this model. The Benz match chamber is known to allow exceptional accuracy without having the finicky nature usually associated with tight match chambers.

The widely-available CCI Standard Velocity rounds have become my favorite everyday round, as they consistently give me 10-20 shot groups of only .5” at 50 yards, but Lapua Center X, Xact, and SK Standard also delivered exceptional results with some impressive .124” 5-shot 50-yard groups.

I find Magnum Research 10/22 rifles to be extremely reliable, and I had no ammo-related malfunctions with this rifle.

The question you have to ask yourself is whether you want a custom $1200 showy match rifle that shoots match ammo really well, or for half the price a Magnum Research rifle that’s light, includes the most popular features, shoots Mini-Mags and CCI Standard Velocity ammo well, and is ready for the next-level trigger upgrade whenever you are.

Even when adding a top end optic such as this LUCID and a Timney trigger, you’ll still drop less than $1000 for a 10/22 rig which almost matches up to rigs that cost $500 more.

Final Thoughts

This is an accurate and reliable setup, but it does not have the finish quality and refinement of a Force or Kidd custom 10/22. It is clear to me that Magnum Research wanted to produce a good rifle at a competitive price, and they did. It makes you wonder why anyone would buy a heavy, cumbersome, more-expensive rifle.

The MLR22ATU is far from a beginners gun and will hang with top-end rigs almost shot-for-shot — even with less-expensive ammo. It packs in everything on an ultimate 10/22 wishlist (with the exception of a match trigger) into a $599 rifle (street price hovers around $500).

I believe Magnum Research has chosen a sweet spot in creating a rifle to be used, scratched, scraped, bumped, and flogged in the field and on the range, and even serve as a light training rifle for youngsters.

Manufacturer Specs

• Model: MLR22ATU
• Caliber: 22LR
• Barrel: 18″ stainless steel, tensioned, aluminum sleeve, with 1:16 twist
• Weight: 4 lbs 8 oz
• Length: 36 1/8” overall
• Length of Pull: 13-⅝”
• Sights: None (Integral Scope Base)
• Stock: Ambidextrous Thumbhole Stock
• Magazine: One 10-Round Ruger Rotary 10/22 Magazine

The post Review: Magnum Research 22LR MLR-22ATU Rimfire Rifle appeared first on AllOutdoor.com.

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Review: Magnum Research 22LR MLR-22ATU Rimfire Rifle

Whenever you buy something with a promise of "Lifetime" service, the question is exactly how long that will last. For owners of the very first TiVo DVRs who shelled out for promised Lifetime service, the answer is about 17 years. Dave Zatz let us know the company is notifying owners that after September 29th, their boxes will no longer be able to create recordings or pull down guide data. The Series1 boxes won’t be able to handle guide data provided by TiVo’s new owner Rovi, which is why it’s ending service.

TiVo:

TiVo is upgrading the data associated with content from a user’s cable package. The original TiVo Series1 DVR released more than a decade ago, will not operate with current software versions and will no longer be supported by the TiVo service.

TiVo Series 1 "Lifetime" Service lasted about 16 years. http://pic.twitter.com/zjToqMsXvv

— Dave Zatz (@davezatz) August 16, 2016

For its part, TiVo says there are about 3,500 active Series1 DVRs still going, and it’s offering owners a $75 prepaid Visa card. If that’s not enough to make them happy, then they may not have much in the way of legal recourse, because, as ZatzNotFunny pointed out in 2013, the company changed its Terms of Service to include a class action/jury trial waiver and mandating arbitration, unless owners opted out within 90 days.

Once upon a time, owners could transfer their lifetime service to a newer box, but those days have passed. Series1 service in the US lasted about five years longer than it did in the UK, where service shut down in early 2011. Once September is over the box won’t quite turn into a paperweight — it will function but only in very basic ways for watching live TV or existing recordings, and navigating with just the channel up/down buttons. To create a new recording without guide data, owners would need to manually program the date, channel number and start/end time.

All of TiVo’s newer hardware will be upgraded to work with the new data streams, although it is a reminder that any cloud-connected devices you own could be on the chopping block someday.

Source: TiVo Community

via Engadget
TiVo is pulling the plug on Series 1 DVRs September 29th

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Defensive Gun Use of the Day: AZ Open Carrier Shoots, Kills Armed Felon