Design canvas — pick every knob

Every concept in the curriculum is a knob; a workload determines which positions of those knobs are correct, and bad combinations have predictable failure modes.

Previously

Every primitive is now on the table; the question is which positions of the knobs survive a real workload.

Scene 13

Design canvas: pick every knob

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natural key → wide partitions on hot users

CL_write=ALL kills availability →

1 vnode/node → lopsided ring

What to watch for

The defaults — raw partition key, CL_write=ALL, 1 vnode/node — are wrong on purpose for the timeseries brief. The verifier panel is glowing red on the knobs that will hurt first. Read it, then continue to start tuning.

Implementation

Highlighted lines are the ones running in the diagram right now.

Verifier.verify

grade each knob against the chosen workload

1def verify(workload, choices):
2    return [
3        verify_partition_key(workload, choices),
4        verify_rf(workload, choices),
5        verify_cl_write(workload, choices),
6        verify_cl_read(workload, choices),
7        verify_vnodes(workload, choices),
8        verify_multi_dc(workload, choices),
9    ]

Verifier.verify_cl_write

the same W is right or wrong depending on the brief

1def verify_cl_write(workload, c):
2    if workload == 'timeseries':
3        if c.cl_write == 'ALL': return fail
4        if c.cl_write in {'QUORUM', 'LOCAL_QUORUM'}:
5            return ok
6        return warn  # ONE: no read-your-writes
7    if workload == 'multi-region-kv':
8        if c.cl_write == 'LOCAL_QUORUM': return ok
9        if c.cl_write == 'ALL': return fail
10        return warn
11    # write-heavy-ingest
12    return ok if c.cl_write == 'ONE' else warn

Verifier.verify_partition_key

wide-partition guard — bucketed for timeseries, raw for KV

1def verify_partition_key(workload, c):
2    if workload == 'timeseries':
3        if c.partition_key == 'time-bucketed':
4            return ok  # bounded; TWCS-friendly
5        if c.partition_key == 'natural':
6            return fail  # >100MB partitions
7        return warn
8    if workload == 'multi-region-kv':
9        if c.partition_key == 'natural': return ok
10        return warn  # KV access by id
11    # write-heavy-ingest
12    return ok  # composite or time bucketing

Where this sits in Build a wide-column store (Cassandra / DynamoDB family)

Scene 12 of 13, in the Design canvas act — Pick every knob against a workload and grade the result.. Given a real workload, pick partition key, RF, W/R, vnodes, and DC topology — and grade the result.

All 13 scenes in Build a wide-column store (Cassandra / DynamoDB family) · Every curriculum

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Every scene in Build a wide-column store (Cassandra / DynamoDB family) builds on the one before it.All 13 Build a wide-column store (Cassandra / DynamoDB family) scenes