I want to verify that rows are getting added to the table. What cql statement would show the last n rows from the table below?
Table description below:
cqlsh:timeseries> describe table option_data;
CREATE TABLE option_data (
ts bigint,
id text,
strike decimal,
callask decimal,
callbid decimal,
maturity timestamp,
putask decimal,
putbid decimal,
PRIMARY KEY ((ts), id, strike)
) WITH
bloom_filter_fp_chance=0.010000 AND
caching='KEYS_ONLY' AND
comment='' AND
dclocal_read_repair_chance=0.100000 AND
gc_grace_seconds=864000 AND
index_interval=128 AND
read_repair_chance=0.000000 AND
replicate_on_write='true' AND
populate_io_cache_on_flush='false' AND
default_time_to_live=0 AND
speculative_retry='99.0PERCENTILE' AND
memtable_flush_period_in_ms=0 AND
compaction={'class': 'SizeTieredCompactionStrategy'} AND
compression={'sstable_compression': 'LZ4Compressor'};
cqlsh:timeseries>
You didn't specify last n "by what".
To get the last N per id:
SELECT * FROM option_data WHERE ts=1 ORDER BY id DESC LIMIT N;
ORDER BY clause can only be applied to the second column in a compound primary key. If you need to query by time you will need to think about your data model a little more.
If your queries are most often "last N", you might consider writing something like this:
CREATE TABLE time_series (
id text,
t timeuuid,
data text,
PRIMARY KEY (id, t)
) WITH CLUSTERING ORDER BY (t DESC)
... where 'id' is your time series id. The CLUSTERING ORDER reverses the order of timeuuid 't', causing the cells to be stored in a natural order for your query.
With this, you would get the last five events as follows:
SELECT * FROM time_series WHERE id='stream id' LIMIT 5;
There is a lot of information out there for time series in Cassandra. I suggest reading some of the more recent articles on the matter.
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