cassandra 시간정보 저장

cassandra 에서 시간 정보를 저장할 때, 3가지 type으로 저장가능하다. 

1. uuid

2. timeuuid

3. timestamp

uuid에서 나온 것이 timeuuid 이다. uuid (timeuuid)의 큰 장점은 표준 uuid 라는 점, dateOf나 unixTimestampOf function을 cql에서 사용할 수 있다. 반면, timestamp에서는 이를 쓸 수 없다. timeuuid 는 처음부터 time으로 sorting이 가능하다. time uuid type으로 comparator type을 지정할 수 있다.

timeuuid는 mac address 기반이다.. 따라서 time stamp를 쓸지 timeuuid를 쓸지 고민해야 한다. 

http://www.datastax.com/documentation/cql/3.0/webhelp/index.html#cql/cql_reference/cql_data_types_c.html?pagename=docs&version=1.2&file=cql_cli/cql_data_types

timestamp	integers, strings	Date plus time, encoded as 8 bytes since epoch
uuid	uuids	A UUID in standard UUID format
timeuuid	uuids	Type 1 UUID only (CQL 3)

http://www.datastax.com/documentation/cql/3.0/webhelp/index.html#cql/cql_reference/cql_lexicon_c.html#reference_ds_rgn_xy5_yj  

• uuid

  32 hex digits, 0-9 or a-f, which are case-insensitive, separated by dashes, -, after the 8th, 12th, 16th, and 20th digits. For example: 01234567-0123-0123-0123-0123456789ab

• timeuuid

  Uses the time in 100 nanosecond intervals since 00:00:00.00 UTC (60 bits), a clock sequence number for prevention of duplicates (14 bits), plus the IEEE 801 MAC address (48 bits) to generate a unique identifier. For example: d2177dd0-eaa2-11de-a572-001b779c76e3

  
  

  
  

  
  

http://stackoverflow.com/questions/17945677/cassandra-uuid-vs-timeuuid-benefits-and-disadvantages

UUID and TIMEUUID are stored the same way in Cassandra, and they only really represent two different sorting implementations.

TIMEUUID columns are sorted by their time components first, and then by their raw bytes, whereasUUID columns are sorted by their version first, then if both are version 1 by their time component, and finally by their raw bytes. Curiosly the time component sorting implementations are duplicated betweenUUIDType and TimeUUIDType in the Cassandra code, except for different formatting.

I think of the UUID vs. TIMEUUID question primarily as documentation: if you choose TIMEUUIDyou're saying that you're storing things in chronological order, and that these things can occur at the same time, so a simple timestamp isn't enough. Using UUID says that you don't care about order (even if in practice the columns will be ordered by time if you put version 1 UUIDs in them), you just want to make sure that things have unique IDs.

Even if using NOW() to generate UUID values is convenient, it's also very surprising to other people reading your code.

It probably does not matter much in the grand scheme of things, but sorting non-version 1 UUIDs is a bit faster than version 1, so if you have a UUID column and generate the UUIDs yourself, go for another version.

http://wiki.apache.org/cassandra/FAQ#working_with_timeuuid_in_java

http://svn.apache.org/repos/asf/cassandra/trunk/src/java/org/apache/cassandra/db/marshal/TimeUUIDType.java

http://www.datastax.com/docs/0.8/dml/using_cli

[default@demo] CREATE COLUMN FAMILY blog_entry
WITH comparator = TimeUUIDType
AND key_validation_class=UTF8Type 

AND default_validation_class = UTF8Type;