在Cassandra中存储最后一次接触时间的最佳方法

Question

我想要的桌子：

CREATE TABLE ksp1.user_last_job_activities (
    user_id bigint,
    touched_at timeuuid,
    PRIMARY KEY (user_id, touched_at)
) WITH CLUSTERING ORDER BY (touched_at DESC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = '{"keys":"ALL", "rows_per_partition":"NONE"}'
    AND comment = ''
    AND compaction = {'min_threshold': '4', 'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32'}
    AND compression = {'sstable_compression': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99.0PERCENTILE';

更新

谢了！我做了一些关于writetime的实验，因为我无论如何都要写值，所以我只写时间。

CREATE TABLE simple_user_last_activity (
    user_id bigint,
    touched_at timestamp,
    PRIMARY KEY (user_id)
);

INSERT INTO simple_user_last_activity (user_id, touched_at) VALUES (6, dateof(now()));
SELECT touched_at from simple_user_last_activity WHERE user_id = 6;

CREATE TABLE final_user_last_job_activities (
    user_id bigint,
    touched_at timestamp,
    job_id bigint,
    PRIMARY KEY (user_id, touched_at)
) 
WITH CLUSTERING ORDER BY (touched_at DESC)
AND default_time_to_live = 604800;

INSERT INTO final_user_last_job_activities (user_id, touched_at, job_id) VALUES (5, dateof(now()), 5);
INSERT INTO final_user_last_job_activities (user_id, touched_at, job_id) VALUES (5, dateof(now()), 6);
INSERT INTO final_user_last_job_activities (user_id, touched_at, job_id) VALUES (5, dateof(now()), 7);
INSERT INTO final_user_last_job_activities (user_id, touched_at, job_id) VALUES (5, dateof(now()), 6);

SELECT * FROM final_user_last_job_activities LIMIT 1;

这给了我：

 user_id | touched_at               | job_id
---------+--------------------------+--------
       5 | 2015-06-17 12:43:30+1200 |      6

简单的基准测试在存储或从更大的表中读取时没有显著的性能差异。

Answer 1

因为C*是最后的write wins，所以您可以简单地保留每行的最新版本。

正如MSD所建议的，您可以使用writetime提取写入时间。但是要小心，因为这是特定于列的，并且不能在主键列上使用写时间。例如，在如下表中：

cqlsh> create TABLE test.test ( a int, b int, c int, d int, primary key (a))
   ... ;
cqlsh> insert INTO  test.test (a, b, c, d) VALUES ( 1,2,3,4)
   ... ;

cqlsh> select * from test.test
   ... ;

 a | b    | c | d
---+------+---+------
 1 |    2 | 3 |    4

(2 rows)

cqlsh> insert into test.test (a,c) values (1, 6);
cqlsh> select * from test.test ;

 a | b    | c | d
---+------+---+------
 1 |    2 | 6 |    4

(2 rows)
cqlsh> select writetime(a), writetime(b), writetime(c), writetime(d) from test.test
   ... ;
InvalidRequest: code=2200 [Invalid query] message="Cannot use selection function writeTime on PRIMARY KEY part a"

cqlsh> select  writetime(b), writetime(c), writetime(d) from test.test  ;

 writetime(b)     | writetime(c)     | writetime(d)
------------------+------------------+------------------
 1434424690700887 | 1434424690700887 | 1434424702420929

否则，可以添加具有时间戳的cql列：

create TABLE test.test ( a int, b int, c int, d int, touched_at timeuuid, primary key (a)) ;