[vitessdriver|vtadmin] Support Ping in vitessdriver, use in vtadmin to healthcheck connections during Dial #7709
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Description
This PR fixes a longstanding issue in vtadmin, where if vtadmin had
Dial
-ed a cluster, obtained a connection to a vtgate, and that vtgate was torn down, that cluster would become unusable without restarting vtadmin, and we would see the following, forever:To fix this, I've introduced the following:
database/sq/driver.Pinger
interface invitessdriver
, which just issues aselect 1
query.Ping
duringVTGateProxy.Dial
in the case where the proxy has a non-nil connection. We set a configurable timeout here, to avoid blocking forever, and if the call fails we attempt to close the connection and then fall through to the "discover new vtgate and dial it" phase of theDial
method. If the ping check succeeds, we know we can just keep using that connection.Related Issue(s)
Checklist
Deployment Notes
Impacted Areas in Vitess
Components that this PR will affect: