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bits28

The bits28 functions provide an API for working with "bit pattern" INT64 fields, as used in the clients_last_seen dataset for desktop Firefox and similar datasets for other applications.

A powerful feature of the clients_last_seen methodology is that it doesn't record specific metrics like MAU and WAU directly, but rather each row stores a history of the discrete days on which a client was active in the past 28 days. We could calculate active users in a 10 day or 25 day window just as efficiently as a 7 day (WAU) or 28 day (MAU) window. But we can also define completely new metrics based on these usage histories, such as various retention definitions.

The usage history is encoded as a "bit pattern" where the physical type of the field is a BigQuery INT64, but logically the integer represents an array of bits, with each 1 indicating a day where the given clients was active and each 0 indicating a day where the client was inactive.

active_in_range (UDF)

Return a boolean indicating if any bits are set in the specified range of a bit pattern. The start_offset must be zero or a negative number indicating an offset from the rightmost bit in the pattern. n_bits is the number of bits to consider, counting right from the bit at start_offset.

See detailed docs for the bits28 suite of functions: https://docs.telemetry.mozilla.org/cookbooks/clients_last_seen_bits.html#udf-reference

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days_since_seen (UDF)

Return the position of the rightmost set bit in an INT64 bit pattern.

To determine this position, we take a bitwise AND of the bit pattern and its complement, then we determine the position of the bit via base-2 logarithm; see https://stackoverflow.com/a/42747608/1260237

See detailed docs for the bits28 suite of functions: https://docs.telemetry.mozilla.org/cookbooks/clients_last_seen_bits.html#udf-reference

SELECT
  mozfun.bits28.days_since_seen(18)
-- >> 1

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from_string (UDF)

Convert a string representing individual bits into an INT64.

Implementation based on https://stackoverflow.com/a/51600210/1260237

See detailed docs for the bits28 suite of functions: https://docs.telemetry.mozilla.org/cookbooks/clients_last_seen_bits.html#udf-reference

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retention (UDF)

Return a nested struct providing booleans indicating whether a given client was active various time periods based on the passed bit pattern.

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to_string (UDF)

Convert an INT64 field into a 28-character string representing the individual bits.

Implementation based on https://stackoverflow.com/a/51600210/1260237

See detailed docs for the bits28 suite of functions: https://docs.telemetry.mozilla.org/cookbooks/clients_last_seen_bits.html#udf-reference

SELECT
  [mozfun.bits28.to_string(1), mozfun.bits28.to_string(2), mozfun.bits28.to_string(3)]
-- >>> ['0000000000000000000000000001',
--      '0000000000000000000000000010',
--      '0000000000000000000000000011']

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to_dates (UDF)

Convert a bit pattern into an array of the dates is represents.

See detailed docs for the bits28 suite of functions: https://docs.telemetry.mozilla.org/cookbooks/clients_last_seen_bits.html#udf-reference

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range (UDF)

Return an INT64 representing a range of bits from a source bit pattern.

The start_offset must be zero or a negative number indicating an offset from the rightmost bit in the pattern.

n_bits is the number of bits to consider, counting right from the bit at start_offset.

See detailed docs for the bits28 suite of functions: https://docs.telemetry.mozilla.org/cookbooks/clients_last_seen_bits.html#udf-reference

SELECT
  -- Signature is bits28.range(offset_to_day_0, start_bit, number_of_bits)
  mozfun.bits28.range(days_seen_bits, -13 + 0, 7) AS week_0_bits,
  mozfun.bits28.range(days_seen_bits, -13 + 7, 7) AS week_1_bits
FROM
  telemetry.clients_last_seen
WHERE
  submission_date > '2020-01-01'

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