NB5 Docs► User Guide▼ Core Op Fields 🖺

Some op template fields are reserved by nb5. These are provided by the runtime, not any particular driver, and can be used in any op template.

👉 op fields can be defined at any level of a workload template with a param property. Op template which do not have this op field by name will automatically inherit it.

Core Op Fields


Each op template in an activity can use a specific driver. If this op field is not provided in the op template, then it is set by default from the activity params. If neither is set, an error is thrown.

Since each op template can have a unique driver, and each activity can have multiple op templates, each activity will have multiple drivers active while it is running. These drivers are instanced and shared between op templates which specify the same driver by name.

During activity initialization, all the drivers which are loaded by active op templates (those not filtered out) are consulted for valid activity params. Only params which are valid for at least one active driver will be allowed to be set on the activity. This includes core activity params.


The space is a named cache of driver state. For each driver, a cache of driver-specific "driver space" objects is kept. If the value is not set in the op template, then the effect is the same as all op templates sharing a single instance of a driver for a given name (Where the name is the same for multiple op templates). However, if the users sets the space op field to a binding, then the driver will be virtualized over the names provided, allowing for a given driver to be effectively multi-instanced within the activity.

👉 Be careful with this op field! The way it works allows for quite advanced testing scenarios to be built with very minimal effort, compared to nearly all other approaches. However, if you set this op field to a binding function which produces a high cardinality values, you will be asking your client to create many instances of a native driver. This is not likely to end well for at least the client, and in some cases the server. This does present interesting stress testing scenarios, however!

When an activity is shutting down, it will automatically close out any driver spaces according to their own built-in shutdown logic, but not until the activity is complete. At present, there is no space cache expiry mechanism, but this can be added if someone needs it.


An op field called ratio can be specified on an op template to set the number of times this op will occur in the op sequence.

When an activity is initialized, all the active statements are combined into a sequence based on their relative ratios. By default, all op templates are initialized with a ratio of 1 if none is specified by the user.

For example, consider the op templates below:

    op: "select foo,bar from baz where ..."
    ratio: 1
    op: "select bar,baz from foo where ..."
    ratio: 2
    op: "select baz,foo from bar where ..."
    ratio: 3

If all ops are activated (there is no tag filtering), then the activity will be initialized with a sequence length of 6. In this case, the relative ratio of op "s3" will be 50% overall. If you filtered out the first op, then the sequence would be 5 operations long. In this case, the relative ratio of op "s3" would be 60% overall. It is important to remember that op ratios are always relative to the total sum of the active ops' ratios.

This op field works closely with the core activity parameter seq


By setting this to true, each named op template will be instrumented with a set of metrics, with the metric name derived from its op name.

For example, with the following workload template:

   op: "example stmt1"
   instrument: true
   op: "example stmt2"
   instrument: true

With instrument enabled for each of these ops, six additional metrics will be created: four timers named op1-success, op1-error, op2-success, and op2-error, and two histograms named op1-result-size and op2-result size.

This is very useful for understanding performance dynamics of individual operations. However, be careful when enabling this for a large number of metrics (by setting it as a doc or block level param), especially when you are running with more than 3 significant digits of HDR histogram precision.



This op fields allow for a timer or set of timers to be started immediately before an operation is started and stopped immediately after another (or the same!) operation is completed. This allows you to instrument your access patterns with arbitrary timers across any number of operations.

These timers are started and stopped unconditionally, which means failed operations will be included. Be sure to correlate your metrics so you know what you are truly measuring.

For example:

    op: "example stmt1"
    start-timers: stanza1, stanza2
    op: "example stmt2"
    stop-timers: stanza1
    op: "example stmt"
    stop-timers: stanza2

In this case, before op1 is executed, a timer is started for stanza1 and stanza2. After op2 has been executed, successful or not, the timer for stanza1 will be stopped. After op3 has been executed, successful or not, the timer named stanza2 will be stopped.

These are treated just like any other timers, with a single named instance per activity, thus the measurements are an aggregate over all threads.

👉 The instancing of these named timers is per-thread! There is no way to cross the streams, so measurements are coherent within serialized operations which represent real access patterns in a given application thread.

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