release-2.1: kv: set sane default for kv.transaction.write_pipelining_max_batch_size #32621
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bdarnell
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Nov 26, 2018
Informs cockroachdb#32522. There is a tradeoff here between the overhead of waiting for consensus for a batch if we don't pipeline and proving that all of the writes in the batch succeed if we do pipeline. We set this default to a value which experimentally strikes a balance between the two costs. To determine the best value for this setting, I ran a three-node single-AZ AWS cluster with 4 vCPU nodes (`m5d.xlarge`). I modified KV to perform writes in an explicit txn and to run multiple statements. I then ran `kv0` with 8 DML statements per txn (a reasonable estimate for the average number of statements that an **explicit** txn runs) and adjusted the batch size of these statements from 1 to 256. This resulted in the following graph: <see graph in PR> We can see that the cross-over point where txn pipelining stops being beneficial is with batch sizes somewhere between 128 and 256 rows. Given this information, I set the default for `kv.transaction.write_pipelining_max_batch_size` to 128. Of course, there are a lot of variables at play here: storage throughput, replication latency, node size, etc. I think the setup I used hits a reasonable middle ground with these. Release note (performance improvement): Change the default value for the cluster setting kv.transaction.write_pipelining_max_batch_size to 128. This speeds up bulk write operations.
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Backport 1/1 commits from #32606.
/cc @cockroachdb/release
Informs #32522.
There is a tradeoff here between the overhead of waiting for consensus for a batch if we don't pipeline and proving that all of the writes in the batch succeed if we do pipeline. We set this default to a value which experimentally strikes a balance between the two costs.
To determine the best value for this setting, I ran a three-node single-AZ AWS cluster with 4 vCPU nodes (
m5d.xlarge). I modified KV to perform writes in an explicit txn and to run multiple statements. I then rankv0with 8 DML statements per txn (a reasonable estimate for the average number of statements that an explicit txn runs) and adjusted the batch size of these statements from 1 to 256. This resulted in the following graph:We can see that the cross-over point where txn pipelining stops being beneficial is with batch sizes somewhere between 128 and 256 rows. Given this information, I set the default for
kv.transaction.write_pipelining_max_batch_size` to 128.
Of course, there are a lot of variables at play here: storage throughput, replication latency, node size, etc. I think the setup I used hits a reasonable middle ground with these.
Release note: None