[CASSANDRA-12431] Getting null value for the field that has value when query result has many rows

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Cannot Reproduce
• Fix Version/s: 2.2.x
• Severity: Normal
• Assignee: Edward Capriolo
• Reporter: Fei Fang

Authors

Edward Capriolo

• Created: 10/Aug/16 17:47
• Updated: 16/Apr/19 09:30
• Resolved: 05/Oct/16 17:31

Description

Hi,
We get null value (not an older value, but null) for a float column (score) from a 20k result row query. However, when we fetch data for that specific row, the column actually has value.
The table schema is like this:

CREATE TABLE IF NOT EXISTS email_histogram (
id text,
email text,
score float,
PRIMARY KEY (id, email)
) WITH bloom_filter_fp_chance = 0.01
AND caching = 'KEYS_ONLY'
AND comment = ''
AND compaction =
{'tombstone_threshold': '0.1', 'tombstone_compaction_interval': '300', 'class': 'org.apache.cassandra.db.compaction.LeveledCompactionStrategy'}
AND compression =
{'sstable_compression': 'org.apache.cassandra.io.compress.SnappyCompressor'}
AND dclocal_read_repair_chance = 0.1
AND default_time_to_live = 864000
AND gc_grace_seconds = 86400
AND memtable_flush_period_in_ms = 0
AND read_repair_chance = 0.0
AND speculative_retry = '99.0PERCENTILE';

This is my read query: SELECT * FROM " + TABLE_NAME + " WHERE guid = ?

I'm using consistency One when querying it and Quorum when updating it. If I insert data, I insert for all the columns, never only part of the column. I understand that I might get out of date value since I'm using One to read, but again here I'm not getting out of date value, but just "null".

This is happening on our staging server which servers 20k users, and we see this error happening 10+ times everyday. I don't have an exact number of how many times we do the query, but nodetool cfstats shows local read count of 85314 for this table for the last 18 hours and we have 6 cassandra nodes in this cluster so about 500k querying for 18 hours.

We update the table every 3 weeks. The table has 20k rows for each key (guid) I'm querying for. Out of the 20k rows, only a couple at most are null and they are not the same every time we query the same key.

We are using C# driver version 3.0.1 and Cassandra version 2.2.6.44.