Get Unix timestamp in Java, Python, Erlang

Mostly a note for myself. To Get Unix timestamp value in seconds

java:

long timestamp = System.currentTimeMillis()/1000


Python:

import time
timestamp = int(time.time())


Erlang:

{Mega, Secs, _} = now(),
Timestamp = Mega*1000000 + Secs,


Working with timestamps in MySQL

mysql> SELECT UNIX_TIMESTAMP('1997-10-04 22:23:00');
-> 875996580
mysql> SELECT FROM_UNIXTIME(1111885200);
+---------------------------+
| FROM_UNIXTIME(1111885200) |
+---------------------------+
| 2005-03-27 03:00:00 |
+---------------------------+


How to produce hex array from binary data

Suppose you have a binary file you want to include as byte array into C/C++/Java program. Here how you can generate it (just add opening and closing braces and clean some garbage at the end)

hexdump -v -e " 16/1 \"0x%02X, \" \"\n\""

Something like the following will be produced:


0x7F, 0xFE, 0xF9, 0xE7, 0x9F, 0x7F, 0xFE, 0xF9, 0xE7, 0x9F, 0x7F, 0xFE, 0xF9, 0xE7, 0x9F, 0x7F,
0xFE, 0xF9, 0xE7, 0x9F, 0x7F, 0xFE, 0x0F, 0xFD, 0x3F, 0x4F, 0xAC, 0x0A, 0xA2, 0x00, 0xB0, 0x94,
0x01, 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x , 0x ,


Disappointment about Hibernate and MySQL

One-to-one unidirectional relation implementation in Hibernate sucks. You implement it using <many-to-one ... unique="true">. This creates two indexes in the table for the same field, one for uniqueness constraint, one for foreign key constraint.

Class inheritance when using table-per-subclass is implemented in similar way, again two indexes per field (ID) in child table, one created as primary key constraint, second as foreign key constraint referencing parent class table.

And finally dropping an index in MySQL InnoDB table is very expensive operation – it creates temporary table and reindexes it with remaining indexes. So if you want to drop 4 indexes it will re-create and re-index table 4 times. This can take many hours on any reasonably large database.

I’m disappointed.