Despite what Comet says, most companies don't GAS about you in the long term, if they get into a tough position, they won't hesitate to let you go with no more than a "sorry, see ya," especially with your time in the industry. I've been at companies where they gave people two weeks severance who had been working there for 10 years.
You need to look out for yourself first - this is just a reality in today's marketplace. You're the only one that's going to look out for your career.
With that said, I've also worked at a company that was exceptionally good to us when it came time for layoffs. So it really varies from company to company. But it's unlikely that after only 8 months you're going to be very high up on any list.
I certainly wouldn't go into my boss' office and say "beat this or I walk" but I would tell him that I got an offer for a new job and that you're thinking of taking it. If he offers to meet or beat it, then you know he values you; if he doesn't, or says "see ya" then you'll know you're probably better off walking now than in 2 years when he needs to lay someone off and you're the lowest on the totem pole.
I don't know what you make, but if you're happy where you're at, confident in the company, and see a career path there for yourself, a 10-15% raise is probably not enough to make it worth changing jobs (at a starting salary level at an early stage in your career). If you hate what you're doing, if it's going nowhere, if your boss is a pr*ick, then it's probably worth taking a pay cut to go elsewhere, so if they're offering you more, jump on it.
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