Loading snapshot id and term + vote involve selecting static
fields from the "system.raft" table, constrained by a given
group id.
The code incorrectly assumes that, for example,
`SELECT snapshot_id FROM raft WHERE group_id=?` in
`load_snapshot` always returns only one row.
This is not true, since this will return a row
for each (pk, ck) combination, which is (group_id, index)
for "system.raft" table.
The same applies for the `load_term_and_vote`, which selects
static `vote_term` and `vote` from "system.raft".
This results in a crash at node startup when there is
a non-empty raft log containing more than one entry
for a given `group_id`.
Restrict the selection to always return one row by applying
`LIMIT 1` clause.
Tests: unit(dev)
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
Message-Id: <20210723183232.742083-1-pa.solodovnikov@scylladb.com>
bcbcc18aa1