Jepsen: TiDB 2.1.7
source link: https://www.tuicool.com/articles/yqiEnem
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TiDB
is a distributed, auto-sharded SQL database based on Google’s Percolator model. Despite promising snapshot isolation, TiDB 2.1.7 through 3.0.0-beta.1-40 allowed read skew and lost updates by default, thanks to two auto-retry mechanisms which blindly re-applied updates when a transaction conflicted. TiDB also supports a select ... for update
statement which mostly, but not entirely, prevents write skew. We found a minor race condition in table creation, reduced durability & fault tolerance in fresh clusters, and several crashes on startup. With both auto-retry mechanisms disabled, TiDB 2.1.8 through 3.0.0-beta.1-40 passed our tests for snapshot isolation and single-key linearizability. 3.0.0-rc.2, which disables auto-retry by default, also passes. Finally, TiDB has a theoretical dependence on CLOCK_MONOTONIC_RAW
for safety, but we have not yet observed anomalies due to clock skew, possibly due to tooling limitations. This work was funded by PingCAP
, the makers of TiDB, and conducted in accordance with theJepsen ethics policy.
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