postgresql – SELECT FOR UPDATE (NOWAIT) on auxilliary table for serializing updates?

Background:

I have an inventory tracking application which needs to avoid the following sort of situation where the same inventory might be used twice due to lack of serialization. The constraint is that each item of inventory from a pool of inventory must in use only once at any given time (much simplified example):

CREATE TABLE inventory_use (id serial, ref varchar);

Transaction 1:
BEGIN;
SELECT * FROM inventory_use;
INSERT INTO inventory_use (ref) VALUES ('T1 insert');

Transaction 2:
BEGIN;
SELECT * FROM inventory_use;
INSERT INTO inventory_use (ref) VALUES ('T2 insert');

Transaction 1:
COMMIT;

Transaction 2:
COMMIT; -- fails (as desired) at SERIALIZABLE, commits (not desired) at REPEATABLE READ

SERIALIZABLE prevents this from occurring by causing the last commit to fail (and REPEATABLE READ does not). However, even though my application does not involve many concurrent writes, I’m reluctant to go for SERIALIZABLE because my understanding of its performance characteristics is weak: I’m not yet confident I know how to predict for example what the effect of concurrent reads or of (read or write) throughput will be on performance, perhaps especially on concurrent transactions that aren’t connected directly with inventory tracking and probably are not critical to the application. Probably I should educate myself more about SERIALIZABLE since it looks very useful, but I’d like to understand the alternatives too.

So this question is about alternative approaches to SERIALIZABLE for this kind of problem, in particular using SELECT FOR UPDATE NOWAIT to serialize inventory tracking updates through row locking while running at the READ COMMITTED isolation level.

What I’ve tried:

I implemented FOR UPDATE NOWAIT locking on the table that records inventory users. That seems to work fine.

However, that may cause trouble because it can block some other updates to that table that need not be serialized. This may well not be critical in my application, but it led me to see if I could use a separate table, created just for the purpose of locking, to do the FOR UPDATE locking. To implement that, before the SELECT FOR UPDATE, I would begin by checking whether an INSERT is needed to represent the pool of inventory whose use needs to be serialized — perhaps via INSERT ... ON CONFLICT DO NOTHING — in order to ensure that there is a suitable row that can be locked to serialize the updates.

Question:

I’ve not been able to find other people using SELECT FOR UPDATE in this style in which:

  1. there is an auxiliary table whose only function is FOR UPDATE row locking, not to store any application data.
  2. FOR UPDATE row locking on existing rows is being used to serialize the creation of new rows

That makes me wonder whether this is a bad way to solve this problem.

I’ve seen other suggested approaches that are similar, for example using REPEATABLE READ with an auxiliary table and using an UPDATE to that table to implicity acquire a lock: https://peter.grman.at/postgres-repeatable-read-vs-serializable/

Is this (the SELECT FOR UPDATE style I describe above) a sensible technique for solving a problem of this kind, and if so, how should it be done? I don’t have specific “how should it be done” issues in mind other than to benefit from experience here.

amazon web services – How to see updates to EBS volume when attached to multiple instances?

I have two ec2 instance running Ubuntu 18.04. I have created a Provisioned IOPS SSD (io1) volume and enabled multi-attach. I have successfully mounted the volume on both instances and can read and write to it without any issues. The problem now is if I modify a file on the shared volume from instance A, I cannot see the change on instance B without remounting the volume. Is there a way to make those updates immediately visible on both instances?

updates – How to find chrome version

Two ways:

  1. Command line (useful for scripting)

Run the Chrome program with the --version command line switch. For example, on macOS:

$  /Applications/Google Chrome.app/Contents/MacOS/Google Chrome --version

Google Chrome 86.0.4240.198
  1. Within the broswer:

Type chrome://settings/help into the location bar.

This can also be accessed through the (“About Chrome” menu item)

In About Chrome, you will find the version information. In Chrome Canary on Mac (mine is 90.0.4390.0 official build), it also checks that you are up to date

Steps to apply windows updates to sql failover cluster?

What are the steps to apply windows updates to a active/passive two node sql failover cluster? My initial thought was to apply windows updates to passive node/reboot and then failover and repeat process but not sure. Do I need to stop the db’s and sql agent jobs before failover?

sql2014
windows 2012r2

sql server – Index with few seeks and many updates

Say I create a nonclustered index on a table. After a week I look at the sats, e.g. number of seeks, scans, updates etc. E.g. say I have 10 seeks and 10000 updates. How can I measure the cost of the 10000 updates? That is how can I measure the cost of the 10000 updates on the nonclustered index vs 10 extra scans on the clustered index?

Google Form – Updates made after release

I created a quiz in Google Forms and released the scores to the students with my feedback. I am a big proponent of students revising their work, so I allow them to “edit after submit.” However, while I can see that that students have edited their responses (see image), I am unable to find where the edited/updated responses are. It only shows me their original answer. The spreadsheet is the same way.
Any help would be greatly appreciated! Updates made after release

updates – Pixel 5 bootloop after flashing patched magisk boot image

I was running Magisk on Android 11 on my Google Pixel 5.
I installed it using a patched boot image from 11.0.0 (RD1A.200810.021.A1, Oct 2020, EU carriers).
Today Android 11 prompted me with an update, I installed it without thinking about the consequences. After rebooting Magisk stopped functioning. So I rebooted to fastboot mode and flashed the same patched boot image as i did the first time. I flashed both boot_a and boot_b, I remembered i did that the last time.

After that the phone is stuck in a boot loop.

I also tried flashing the unpatched boot image from the original image, but same effect.
Maybe i had to patch the latest magisk version on a fresh boot image, but can’t do that anymore without access to magisk on my phone. Was running the latest canary YAHFA version.

Don’t know what to do anymore, really hoping there is a solution without loosing all my data.

pixel 5 fastboot

backup – How to retrieve sms messages that were deleted during november/december 2020 updates? (unrooted)

I have had issues from the last 2 monthly updates (nov/dec 2020), on t-mobile galaxy s9. On the firsst update I lost my several home pages of apps and widgets – everything went blank, but they still existed in apps icon.

Now the second update deleted my sms messages for only 2 weeks – I am missing sms-es before nov 28th then from nov 28th to dec 13th. I just started dating my girl on nov 24th, so I had like to have those messages back. I could take them from her iphone, but I had rather learn this process if at all possible.

My s9 is currently not rooted, but I can root if needed – I am more an enthusiast, rather than an all out power user. I tried a free version of fonepaw, but it only brought up messages I still have access to do (they have a deep scan, but it costs money to do).

I tried doing a restore through google drive and the Samsung restore, but it didn’t provide me the texts. I am open to any suggestions that may work. But this is my first time on this site, so I don’t know if I am explaining too much, or how to best word this body.

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AUTOMATIC XML SITEMAP Search engine spiders will be happy with your ready to go XML sitemap. Automatically updated on a daily basis.

AUTOMATIC SITEMAP Your website sitemap, useful for visitors and search engine spiders, is published and updated automatically.

PRODUCT SEO OPTIMIZER Your products are automatically populated with the correct SEO meta tags and keywords.

FRESH PINGER Search engines and relevant services are automatically pinged to aid in getting your website indexed.

TRAFFIC MAXIMIZER Use our Country Redirect feature to monetize the traffic you get from ALL countries.

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FRESH REVIEWS As well as the reviews from Amazon, you can get your own reviews directly on your store to boost unique content and conversions.

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INTELLIGENT SEARCH Did your visitor search for something not currently in your store? No problem, we will show the results directly from Amazon so you can capture the sale.

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NOTE: The content on a HOME PAGE is unique where the content on the BLOG side of this website is being provided by an auto-blogging and content curation plugin called CyberSyn. This is the RSS aggregator tool used to import RSS feeds and automatically generate WordPress posts for your website from the chosen sources.

If you would like to keep unique content on your blog only, please feel free to delete the plugin, and all the populated articles will be gone from your blog.
SEMrush

Any more questions? Simply send us a message.

 

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No maintenance needed – everything is updated automatically for you multiple times a day.

You have full control over the website using an user-friendly FSI dashboard. Add more products, change the content, tweak the design, see your stats + sales, plus loads more!

Super Easy To Use For Beginners.
The new owner just needs an Amazon Associate and eBay affiliate accounts to collect the earnings (free and easy to set up and we will help you).

The BASEBALL EQUIPMENT niche is highly profitable and a rapidly expanding industry with a huge fan audience.

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The auction winner has the potential to create a great income stream for now and into the future.

BONUS – This also includes 6 months of FREE hosting on the Fresh Store platform worth $114.

BAGS OF PROFIT POTENTIAL!
The main source of income will be made by the Amazon and eBay affiliate programs. The entire site is built using the Amazon and eBay API’s and needs no maintenance.

This is a Proven And Easy Way to start earning money online I am using myself for years.

Other sources of monthly income can include private advertising deals, link sales, and Google Adsense.

SO HOW DO AFFILIATE WEBSITES WORK?
Affiliate websites are a great business model because they require no stock or big upfront investments.

When someone clicks a product on your website, they purchase from Amazon or eBay. You take a commission of the sale, which can be anywhere from around 2% to 15%.

You don’t get any headaches from customers, delivery, stock, etc., and just walk away with your tidy $$$ commissions!

WHAT IS INCLUDED?

Your new website is packed with value:

·Complete Premium affiliate store (BaseballFieldEquipment.com)

·Complete Premium WordPress blog (BaseballFieldEquipment.com/blog)

·Well branded domain name

·6 months of free lightning-fast hosting

·Unique website design
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·Unique content throughout

·Highly profitable niche

·Hand-Picked, Top-Selling products

·Premium Images

·Professional Logo

·100% Ownership

·Fully customizable

·Beginner-friendly admin area

·Premium Support with fast responses

As you may be aware already, it might be challenging to get the Amazon API key right from the start, but as our valued customer, you are allowed to use our Amazon API keys if needed to get you going.

Affiliate Store Features:

FRESH CONNECT Our fast, efficient 100% compliant Amazon API integration has been perfected in over 7 years of development.

FRESH CART Boost commissions with our full-featured shopping cart. Your customers can add multiple products to the basket and checkout when ready.

ZERO STOCK INVESTMENT All the products you sell are shipped from Amazon’s warehouse and you don’t need to invest a dime!

AUTO CONTENT CREATOR Automatically creates unique and readable content for your products when you add them with our built-in content creation.

AMAZON COOKIE BOOSTER Get 90 days of commissions from your customers instead of the usual Amazon 24 hours.

YOUR CATEGORIES Setup your own categories and category groups to help your visitors find what they want to buy.

EASY PRODUCT MANAGER Use your secure dashboard to easily edit individual products or groups of products.

PRODUCT FINDER Uncover the golden products in your niche with our built-in product finder.

EVERY AMAZON COUNTRY Supports all Amazon websites USA, UK, Germany, France, Spain, Canada, Italy, India, China, Japan, and more!

FRESH SYNC Everything is updated for you automatically: product prices, images, key features, descriptions, reviews, and more.

ZERO HASSLE ORDERS Amazon completely handles your orders, the customers, returns, and everything in between.

STORE HEALTH CHECK How do you know your store is running perfectly? Your Store Health page will highlight any issues and give you easy step by step instructions to fix them.

FRESH CACHE TECHNOLOGY We implemented advanced caching in the Amazon API to reduce * throttling * issues and increase speed performance.

PRODUCT IMPORTER Do you know the ASIN numbers? Simply paste them in and everything is added for you.

AUTO POPULATE Want full automation? Simply enter some search keywords and criteria, and products will be added regularly to your store for as long as you wish.

AMAZON REVIEWS Display all the Amazon reviews for your products directly on your store: a guaranteed way to boost conversions.

VISUAL DESIGN EDITOR Make your store look exactly as you want with our visual editor: no coding skills required.

EASY HOMEPAGE DESIGNER You have total control over what goes on your homepage and how it looks.

MOBILE OPTIMIZED Your stores automatically work perfectly for users on any device, meaning better conversions and more sales.

CONTENT CUSTOMIZER Change any content in your store quickly and easily.

YOUR CONTENT Add fresh content of your own to any area of your store.

FULL SIDEBOX CONTROL You decide exactly what goes in your side-box across your store.

AUTOMATIC UPDATES Templates and skins are updated for you automatically.

FRESH SEO ENGINE Your stores are built from the ground up to use solid SEO principles and safe automation.

SOCIAL POSTER – FACEBOOK EDITION Automatically send your products to Facebook pages and get quality, motivated traffic to your store.

SOCIAL POSTER – PINTEREST EDITION Share your products instantly with the savvy and free spending crowd over at Pinterest.

AUTOMATIC XML SITEMAP Search engine spiders will be happy with your ready to go XML sitemap. Automatically updated on a daily basis.

AUTOMATIC SITEMAP Your website sitemap, useful for visitors and search engine spiders, is published and updated automatically.

PRODUCT SEO OPTIMIZER Your products are automatically populated with the correct SEO meta tags and keywords.

FRESH PINGER Search engines and relevant services are automatically pinged to aid in getting your website indexed.

TRAFFIC MAXIMIZER Use our Country Redirect feature to monetize the traffic you get from ALL countries.

SQUEEZE MORE CONVERSIONS Use our Exit Popup tool to show your visitors an offer and tempt them back when they try to leave.

FRESH REVIEWS As well as the reviews from Amazon, you can get your own reviews directly on your store to boost unique content and conversions.

FRESH UPSELL Show related products to your customers either automatically or choose your own.

CURRENCY CONVERTER Change the currency of your products instantly, to whatever you want!

INTELLIGENT SEARCH Did your visitor search for something not currently in your store? No problem, we will show the results directly from Amazon so you can capture the sale.

BASKET BOOSTER Group related products together (Like a BBQ + BBQ Brush + Steaks + Marinade) into Product Bundles to maximize commissions.

CHANGEABLE IMAGES Don’t like the product images from Amazon? No problem, you can add your own directly in your store dashboard.

QUICK EMAIL CAPTURE Capture email addresses into your Store Dashboard or integrate with your favorite email service.

EU COOKIE CONSENT Handle the EU Cookie Regulation laws automatically with this built in and customizable feature.

BONUS! On top of everything, I am giving you a Premium License of WordPress Astra PRO Theme installed for a Blog which is one of the most popular and best-performing themes of all time and costs $249 on its own for a lifetime license.

Using this theme you will have no limits to changing your blog design or anything else you may want to. I am using this theme for most of my own websites.

NOTE: The content on a HOME PAGE is unique where the content on the BLOG side of this website is being provided by an auto-blogging and content curation plugin called CyberSyn.

This is the RSS aggregator tool used to import RSS feeds and automatically generate WordPress posts for your website from the chosen sources.

If you would like to keep unique content on your blog only, please feel free to delete the plugin, and all the populated articles will be gone from your blog.

Any more questions? Simply send us a message.