mysqldump -u devise -ppassword -h 127.0.0.1 database_name > backup.sql

Restore

mysql -u -ppassword database_name < backup.sql

Thought I would write up a bit of advice from the trenches.

Scaling is easy and incredibly difficult at the same time.

Easy in that there is plenty of examples scattered around the web how various people solved their problem. Just use technology X, Y and Z => problem solved.

The hard bit; your problem is most likely similar to, but not exactly the same as someone else. Small differences in architecture and feature set may seem inconsequential when serving 1K of users, but these small differences add up to massively different and complex problems when serving out to thousands/millions of users.

My feeling are a startup should focus on solving the user problem with an insanely great experience. Speed is part of that, but probably not the most important factor with early adopters.

Some thoughts.

1. Hadoop, Hive & similar are fantastic, but really overkill for a startup
2. NoSQL’s are great and fast and all that – but carry the risk of loosing transactional data.
3. MySQL & Postgres, seem no longer cool, but work reliably and can take you far
4. PHP, Rails, Python, & even DotNet all scale (scaling is in the architecture, not language – anyone who tells you otherwise is waving a big red flag that they are not all that clued up on web tech). Of course all can be used to build something that falls over with 5 users.
5. Caching (memcache & similar) is difficult to get right – it is not simple, particularly for logged in users with different access levels, and conducting transactions.
6. Amazon EC2, Google app engine & Heroku – are great to get started – you only pay for the services you use – at some point it will make sense to move to your own infrastructure, or go your own way if your really strapped for cash.
7. Hosting videos and images on Amazon s3 & Cloudfront helps keep infrastructure complexity down, but do cost. One startup I am working with has a couple of thousand users with a bill of around $300 per month for video & image hosting
8. Paypal credit card payments has not been a turnoff – I’ve had two services use it & seen no increase in conversions when replaced with a “named” solution. Web payments can be setup in less than 30 minutes.
9. Validate any advice & thoughts by asking questions and searching for existing answers on www.quora.com. Most things have been discussed a number of times before.
10. Be aware it’s usually where you do not expect to find problems that you come unstuck. For example, your users heavily using parts of your application  in unexpected ways, backing up transaction logs, updating data across multiple servers taking longer than you thought it would.
11. Make sure you have a plan – know your thresholds of tolerance, and have upgrade paths ready to go – you might just get those hundres of thousands/millions of users so be prepared.

So my view is, in the early days, keep things simple and tolerate as little complexity as possible.

Guide as what to measure and set thresholds for.

Budget for around a couple of days to a week to setup a monitoring system. You want to know resource usage trends, as well as if anything out of the ordinary is happening.

Your web site / application

1. How fast home page loads
2. How long various user tasks take (ie: logging in, doing a common tasks)

There are two choices

1. Upgrade to Snow Leopard Server (if you can find a copy & are prepared to shell out $400 or so. Then upgrade to Lion via the app store.
2. Rebuild server as Snow Leopard workstation then upgrade to Lion server vai the app store

Option 1 is the easiest & less painful way to go. You can keep most of your server settings. But it costs $400 or so.

Option 2 is a bit more complex, but you save $400. Here is how I did it.

1. Completely backup the target server – make sure you can access various configuration files
2. Dig out a Snow Leopard install disk
3. Follow these instructions to boot xServer from DVD. Put the Snow Leopard DVD in the optical drive, Use the first blue light option and replace the disk back in the drive when it ejects.
4. Install Snow Leopard & do all the software updates
5. Install Lion the App store, then reboot before the next step
6. Install Lion Server upgrade from App store
7. Restore server settings

Took about a day to complete.

1. Simple message
2. Form to collect emails address
3. Thanks & opportunity to share/recommend

1 Simple Message

Can a user answer these 3 questions:

1. What am I getting
2. How do I get it
3. Why I can’t live without it

If not, then maybe consider changing your landing page.

2. Form to Collect Email Address

Try and have as little information collection as possible (email, password & password Confirmation)

3. Thank user and opportunity to share/recommend

Ok, so not exactly on the landing page, but on the after-submission page (after the user has provided their email address) Thank the user the for their submission, then give them the change to share the offer (facebook, twitter, linked-in, etc).

The mean is the average price movement, whilst the standard deviation tells us how far the price moved. Using these figures (& volatility which is a measure of how fast the price is expected to move), we can model the distribution of expected price movements.

Of course, expected is not the same thing as actual; which always makes things a bit more interesting.

Next up, the Black Scholes model.

Cancan (thanks Ryan Bates) allows role based permission management. Once you understand how things work together, it’s quite easy to setup and test.

Found these blog posts helpful.

http://www.tonyamoyal.com/2010/07/28/rails-authentication-with-devise-and-cancan-customizing-devise-controllers/comment-page-1/#comments

http://www.tonyamoyal.com/2010/09/29/rails-authentication-with-devise-and-cancan-part-2-restful-resources-for-administrators/

There are a few gaps though, that are filled in here.

http://stackoverflow.com/questions/5739419/checkboxes-are-getting-but-not-putting-many-to-many-roles

1. Exercise price
2. Time to expiration
3. Price of underlying
4. Interest rates
5. Dividends
6. Volatility

­­

1. Exercise price

Price at which the underlying can be bought (call) or sold (put). For example for an AAPL 120 strike June contract, means the buyer can purchase 100 share of AAPL for $120 per share, up and until June expiry date.

2. Time to expiration

Every option, traded on an options exchange, has an expiry date. Time to expiration is the number of days until that expiry date.

3. Price of underlying

Price of the underlying shares. This will be continually changing during each trading day, and correspondingly the value of any Options contracts will be changing.

4. Interest Rates

Money used to purchase an option could earn interest sitting in a bank account. Usually the risk free interest rate is used (Rate of Government backed term deposits or similar).

5. Dividends

Some stocks will pay a dividend during the options period. This will effect the underlying price, and thus the options price. Although dividend payment amounts do vary, pricing calculations are usually based upon a historical payment pattern

Holders of options do not receive dividends, only holders of the underlying shares.

6. Volatility

Can be a difficult concept to master. It can be thought of as the markets expectation of the speed of change in an underlying’s price. A high volatility means the market expects the underlying price to change rapidly. A low volatility means the market is not expecting an underlying’s price to change rapidly.

Remember the characteristics of an option. Buying a call or put option contract over a stock, gives you the right to buy (call) or sell (put) 100 shares of the underlying stock, at a certain price, on or before a set date in the future.

Speculation

So if you believe that a stock will rise in the future, instead of purchasing the stock, you can purchase a call option (I prefer long term options for this strategy).

Why do this?

Let’s walk through an example.

Say AAPL is trading at $100 and I believe that this stock will be trading at $150 in 12 months time. To purchase the underlying stock, I would have to pay $100 per share and take the risk of a fluctuating stock price. Purchasing 100 shares will cost $10,000.

12 Month 140 strike Call options are trading at $2 per share. I can purchase 1 of these  for $200 (one options contract refers to 100 shares). This is significantly less capital than $10,000.

My maximum possible loss for this trade is $200 (plus commissions). To make a profit AAPL will need to trade over $142 (140 strike + $2 option contract cost per share).

If I purchased 100 shares of the underlying, at a cost of $10,000, my maximum loss is could be $10,000. I also have to manage the trade, in case the shares dip for some reason.

There are pro’s and con’s, of using Options to speculate. I like the known level of risk & less need to manage the trade.

Insurance / Hedging

Options can be used to protect profits in the case of an unexpected market reversal.

Let’s use the example of AAPL again.

I have 100 AAPl shares, currently trading at $100, I purchased these at $80, meaning I have a $20 per share profit.

I believe that AAPL will continue to rise and so I don’t want to sell the shares and take my profits. I could hedge or insure my position, by buying a 12 month $100 Put option. This gives me the right to sell my shares at $100 at any time for the next 12 months time. The Put option will cost whatever the market is valuing those options at the time. If the Put option costs $4 per share, I have “locked-in” a profit of $16 per share (my $20 dollar profit per share, less the $4 per share cost of the option).

If AAPL falls to $90 before expiry, my Put option still gives me the right to sell my shares at $100, and I still make a profit of $16 on my original $80 purchase prices.

If AAPL rises to $140, I will let the Put option expiry un-exercised as I can sell the shares on the open market for $140, rather than through the option price of $100.

So for a $4 per share expenditure, I have protected a profit of $16 per share. When the Put option expires I can purchase another one (similar to car insurance), close out my position, or do nothing.