[CASSANDRA-98] Reads (get_column) miss data or return stale values if a memtable is being flushed

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 0.3

Environment

all

• Severity: Normal
• Assignee: Sandeep Tata
• Reporter: Sandeep Tata

Authors

Sandeep Tata

• Created: 23/Apr/09 22:08
• Updated: 16/Apr/19 09:33
• Resolved: 24/Apr/09 00:52

Description

Reads can return missing values (null/exception) or find stale copies of a column if the read happens during an SSTable flush.

The get_column can go in, and not find the data in the current memtable. When it looks in the "historical" memtable, if that CF has already been flushed, then it gets cleared from the historical memtable. As a result, the read looks for the column in older SSTables and finds a stale value (if it exists) or returns with null.

It can be tricky to reproduce this problem, but the reason is pretty easy to see.

While subsequent reads might return the correct value (from disk), this behavior makes it very difficult for apps that expect to "read your writes", at least in the absence of failures.