add a cron job to clean up failed merge shards
dcs-web: add /queryz handler for introspecting state
move query transformation code out of per-backend function
handle backend failures _during_ a query (timeouts, EOFs, …)
queryz: use a table for better alignment
add support for cancelling queries
properly mark queries as failed on internal errors, export varz
describe -query_results_path
increase timeout to 200ms, doesn’t always work otherwise
add error message for “failed” type errors