Understand your Mac and iPhone more deeply by tracing the evolution of Mac OS X from prelease to Swift. John Siracusa delivers the details.
You've got two main options:
What exactly is "iowait"? | |
To summarize it in one sentence, 'iowait' is the percentage | |
of time the CPU is idle AND there is at least one I/O | |
in progress. | |
Each CPU can be in one of four states: user, sys, idle, iowait. | |
Performance tools such as vmstat, iostat, sar, etc. print | |
out these four states as a percentage. The sar tool can | |
print out the states on a per CPU basis (-P flag) but most |
I was at Amazon for about six and a half years, and now I've been at Google for that long. One thing that struck me immediately about the two companies -- an impression that has been reinforced almost daily -- is that Amazon does everything wrong, and Google does everything right. Sure, it's a sweeping generalization, but a surprisingly accurate one. It's pretty crazy. There are probably a hundred or even two hundred different ways you can compare the two companies, and Google is superior in all but three of them, if I recall correctly. I actually did a spreadsheet at one point but Legal wouldn't let me show it to anyone, even though recruiting loved it.
I mean, just to give you a very brief taste: Amazon's recruiting process is fundamentally flawed by having teams hire for themselves, so their hiring bar is incredibly inconsistent across teams, despite various efforts they've made to level it out. And their operations are a mess; they don't real
-- show running queries (pre 9.2) | |
SELECT procpid, age(clock_timestamp(), query_start), usename, current_query | |
FROM pg_stat_activity | |
WHERE current_query != '<IDLE>' AND current_query NOT ILIKE '%pg_stat_activity%' | |
ORDER BY query_start desc; | |
-- show running queries (9.2) | |
SELECT pid, age(clock_timestamp(), query_start), usename, query | |
FROM pg_stat_activity | |
WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%' |
WITH table_scans as ( | |
SELECT relid, | |
tables.idx_scan + tables.seq_scan as all_scans, | |
( tables.n_tup_ins + tables.n_tup_upd + tables.n_tup_del ) as writes, | |
pg_relation_size(relid) as table_size | |
FROM pg_stat_user_tables as tables | |
), | |
all_writes as ( | |
SELECT sum(writes) as total_writes | |
FROM table_scans |
** Find commmonly accessed tables and their use of indexes: | |
SELECT relname,seq_tup_read,idx_tup_fetch,cast(idx_tup_fetch AS numeric) / (idx_tup_fetch + seq_tup_read) AS idx_tup_pct FROM pg_stat_user_tables WHERE (idx_tup_fetch + seq_tup_read)>0 ORDER BY idx_tup_pct; | |
Returns output like: | |
relname | seq_tup_read | idx_tup_fetch | idx_tup_pct | |
----------------------+--------------+---------------+------------------------ | |
schema_migrations | 817 | 0 | 0.00000000000000000000 | |
user_device_photos | 349 | 0 | 0.00000000000000000000 |
Rich Hickey • 3 years ago
Sorry, I have to disagree with the entire premise here.
A wide variety of experiences might lead to well-roundedness, but not to greatness, nor even goodness. By constantly switching from one thing to another you are always reaching above your comfort zone, yes, but doing so by resetting your skill and knowledge level to zero.
Mastery comes from a combination of at least several of the following:
(by @andrestaltz)
If you prefer to watch video tutorials with live-coding, then check out this series I recorded with the same contents as in this article: Egghead.io - Introduction to Reactive Programming.
Latency Comparison Numbers | |
-------------------------- | |
L1 cache reference 0.5 ns | |
Branch mispredict 5 ns | |
L2 cache reference 7 ns 14x L1 cache | |
Mutex lock/unlock 25 ns | |
Main memory reference 100 ns 20x L2 cache, 200x L1 cache | |
Compress 1K bytes with Zippy 3,000 ns 3 us | |
Send 1K bytes over 1 Gbps network 10,000 ns 10 us | |
Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD |
It's a common confusion about terminal colours... Actually we have this:
printf "\x1b[${bg};2;${red};${green};${blue}m\n"