Create skipping indexes on observations and analysis tables

[hellais]

Currently the observations and analysis tables don't have complete indexes. We should create the following ones:

ALTER TABLE obs_web ON CLUSTER oonidata_cluster ADD INDEX measurement_start_time_idx measurement_start_time TYPE minmax GRANULARITY 2;
ALTER TABLE obs_web ON CLUSTER oonidata_cluster ADD INDEX probe_cc_idx probe_cc TYPE minmax GRANULARITY 1;
ALTER TABLE obs_web ON CLUSTER oonidata_cluster ADD INDEX probe_asn_idx probe_asn TYPE minmax GRANULARITY 1;

ALTER TABLE analysis_web_measurement ON CLUSTER oonidata_cluster ADD INDEX probe_asn_idx probe_asn TYPE minmax GRANULARITY 1;

And then re-index the data using:

ALTER TABLE obs_web ON CLUSTER oonidata_cluster MATERIALIZE INDEX measurement_start_time_idx;
ALTER TABLE obs_web ON CLUSTER oonidata_cluster MATERIALIZE INDEX probe_cc_idx;
ALTER TABLE obs_web ON CLUSTER oonidata_cluster MATERIALIZE INDEX probe_asn_idx;
ALTER TABLE analysis_web_measurement ON CLUSTER oonidata_cluster MATERIALIZE INDEX probe_asn_idx;