public void shutdown() {
        disconnect();
        destroy();
        isConnected.set(false);
        isTryingToConnect.set(false);
    }
Builds the "compiled" set clause of an update query.
Here, all the pre-processing that can be done prior to receiving the update event is done,
so that such pre-processing work will not be done at each update-event-arrival.

@param updateSet                   the set of assignment expressions, each containing the table column to be
                                   updated and the expression to be assigned.
@param matchingMetaInfoHolder      the meta structure of the incoming matchingEvent
@param variableExpressionExecutors the list of variable ExpressionExecutors already created
@param tableMap                    map of event tables
@param siddhiQueryContext          current siddhi query context
@return CompiledUpdateSet
modules/siddhi-core/src/main/java/io/siddhi/core/table/Table.java