Enable use of 'unset' values in prepared statements by default

[penberg]

We have support for the use of 'unset' values to reduce the number of prepared statements as of commit b432a08. However, user needs to explicitly enable that with the -u command line option, which they will easily forget to do.

We should make this enabled by default just like we do for prepared statements and batching since commit b382110. @haaawk did want us to check the performance impact of 'unset' before we do that, though.

[haaawk]

It would probably be good as the default option should be the one that performs better. I won't insist though :)

[penberg]

@haaawk No, I think it's a reasonable requirement before defaulting to the new option.

[haaawk]

@penberg @elcallio I would wait with enabling this by default. I was testing sstable loader with data generated by cassandra stress. Default schema is:

CREATE KEYSPACE keyspace1 WITH replication = {'class': 'SimpleStrategy', 'replication_factor': '1'} AND durable_writes = true;

CREATE TABLE keyspace1.counter1 (
key blob,
column1 text,
"C0" counter static,
"C1" counter static,
"C2" counter static,
"C3" counter static,
"C4" counter static,
value counter,
PRIMARY KEY (key, column1)
) WITH COMPACT STORAGE
AND CLUSTERING ORDER BY (column1 ASC)
AND bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'enabled': 'false'}
AND crc_check_chance = 1.0
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 = '99PERCENTILE';

CREATE TABLE keyspace1.standard1 (
key blob PRIMARY KEY,
"C0" blob,
"C1" blob,
"C2" blob,
"C3" blob,
"C4" blob
) WITH COMPACT STORAGE
AND bloom_filter_fp_chance = 0.01
AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
AND comment = ''
AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32', 'min_threshold': '4'}
AND compression = {'enabled': 'false'}
AND crc_check_chance = 1.0
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 = '99PERCENTILE';

and running sstable loader like this: ./bin/sstableloader -u -d 127.0.0.1 /home/haaawk/.ccm/loader-1/node1/data0/keyspace1/standard1-c17511f0bb2111e8ac3f47eff2803657/

generates lots of errors:

com.datastax.driver.core.exceptions.InvalidQueryException: Unknown identifier column1