Links for 2016-12-12

  •, MySQL and UTF-8

    good preso from Percona Live 2015 on the messiness of MySQL vs UTF-8 and utf8mb4

    (tags: utf-8 utf8mb4 mysql storage databases slides character-sets)

  • tdunning/t-digest

    A new data structure for accurate on-line accumulation of rank-based statistics such as quantiles and trimmed means. The t-digest algorithm is also very parallel friendly making it useful in map-reduce and parallel streaming applications. The t-digest construction algorithm uses a variant of 1-dimensional k-means clustering to product a data structure that is related to the Q-digest. This t-digest data structure can be used to estimate quantiles or compute other rank statistics. The advantage of the t-digest over the Q-digest is that the t-digest can handle floating point values while the Q-digest is limited to integers. With small changes, the t-digest can handle any values from any ordered set that has something akin to a mean. The accuracy of quantile estimates produced by t-digests can be orders of magnitude more accurate than those produced by Q-digests in spite of the fact that t-digests are more compact when stored on disk.
    Super-nice feature is that it’s mergeable, so amenable to parallel usage across multiple hosts if required. Java implementation, ASL licensing.

    (tags: data-structures algorithms java t-digest statistics quantiles percentiles aggregation digests estimation ranking)

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