Module workload_phase 

Workload phase residuals.

The mix of query digests (statement classes) shifts over time as ETL windows, reporting bursts, and ad-hoc spikes overlap. We track this with one residual per time bucket: the Jensen–Shannon divergence between the current digest-mix histogram and the rolling reference histogram. JS is bounded in [0, 1], symmetric, and zero when distributions agree — exactly the properties the motif state machine needs to call a phase transition.

MySQL Performance Schema digests (fact #19), SQL Server sys.dm_exec_query_stats grouped by query_hash, PostgreSQL pg_stat_statements.queryid all provide statement-class identifiers compatible with this construction.

Functions

js_divergence

Compute Jensen–Shannon divergence (base 2, in [0, 1]) between two digest-mix histograms p and q. Inputs do not need to be normalised; they are renormalised internally.

push_jsd

Push a phase residual at t. bucket_id identifies the time bucket (e.g. an ISO-week or a 5-minute window).