Before this patch, a DistSQL flow running on its gateway node would use the RootTxn for all its processors for row-based flows / all of its operators for vectorized flows if there are no remote flows. Some of these processors/operator can execute concurrently with one another. RootTxns don't support concurrent requests (see cockroachdb#25329), resulting in some reads possibly missing to see the transaction's own writes. This patch fixes things by using a LeafTxn on the gateway in case there's concurrency on the gateway or if there's any remote flows. In other words, the Root is used only if there's no remote flows and no concurrency. This is sufficient for supporting mutations (which need the Root), because mutations force everything to be planned on the gateway and so, thanks to the previous commit, there's no concurrency if that's the case. Fixes cockroachdb#40487 Touches cockroachdb#24798 Release justification: Fixes bad bugs. Release note: Fix a bug possibly leading to transactions missing to see their own previous writes (cockroachdb#40487).

Commits

Commits on Oct 5, 2019

sql: use RootTxn for all flows that don't have remotes

colexec: rename UnorderedSynchronizer

sql: serialize unordered syncs and fuse ordered sync inputs

sql: use LeafTxn for some gateway flows