What does "PER PARTITION LIMIT" means in cql query in cassandra?

[Check Peck]

I have a scylla table as shown below:


    cqlsh:sampleks> describe table test;


    CREATE TABLE test (

        client_id int,

        when timestamp,

        process_ids list<int>,

        md text,

        PRIMARY KEY (client_id, when) ) WITH CLUSTERING ORDER BY (when DESC)

        AND bloom_filter_fp_chance = 0.01

        AND caching = {'keys': 'ALL', 'rows_per_partition': 'ALL'}

        AND comment = ''

        AND compaction = {'class': 'TimeWindowCompactionStrategy',
'compaction_window_size': '1', 'compaction_window_unit': 'DAYS'}

        AND compression = {'sstable_compression':
'org.apache.cassandra.io.compress.LZ4Compressor'}

        AND crc_check_chance = 1.0

        AND dclocal_read_repair_chance = 0.1

        AND default_time_to_live = 0

        AND gc_grace_seconds = 172800

        AND max_index_interval = 1024

        AND memtable_flush_period_in_ms = 0

        AND min_index_interval = 128

        AND read_repair_chance = 0.0

        AND speculative_retry = '99.0PERCENTILE';


And I see this is how we are querying it. It's been a long time I worked on
cassandra so this “PER PARTITION LIMIT” is new thing to me (looks like
recently added). Can someone explain what does this do with some example in
a layman language? I couldn't find any good doc on that which explains
easily.


    SELECT * FROM test WHERE client_id IN ? PER PARTITION LIMIT 1;