HdrHistogram_c: 'C' port of High Dynamic Range (HDR) Histogram

HdrHistogram

This port contains a subset of the functionality supported by the Java implementation. The current supported features are:

• Standard histogram with 64 bit counts (32/16 bit counts not supported)
• All iterator types (all values, recorded, percentiles, linear, logarithmic)
• Histogram serialisation (encoding version 1.2, decoding 1.0-1.2)
• Reader/writer phaser and interval recorder
• Sparse histogram (hdr_packed_histogram, see include/hdr/hdr_packed_histogram.h): a separate, opt-in type whose storage grows with the number of populated buckets, with counts kept in 1, 2, 4 or 8 bytes as needed. Much smaller when you hold many sparsely populated histograms, at the cost of slower recording and no atomic recording; it serialises to the standard compressed format

Features not supported, but planned

• Auto-resizing of histograms

Features unlikely to be implemented

• Double histograms
• Atomic/Concurrent histograms
• 16/32 bit histograms

Embedding the library (minimal static core without zlib/threads, custom allocator, disabling the AVX2 scan): see docs/EMBEDDING.md.

To vendor the library as a few generated files instead of the whole tree, an amalgamation is attached to each release and generated by script/amalgamate.py: the core on its own (hdr_histogram.c and hdr_histogram.h), or with the log codec (--with-log), and for trees that keep the headers in a hdr/ directory (--include-prefix hdr/); see docs/AMALGAMATION.md.

Simple Tutorial

Recording values

#include <hdr_histogram.h>

struct hdr_histogram* histogram;

// Initialise the histogram
hdr_init(
    1,  // Minimum value
    INT64_C(3600000000),  // Maximum value
    3,  // Number of significant figures
    &histogram)  // Pointer to initialise

// Record value
hdr_record_value(
    histogram,  // Histogram to record to
    value)  // Value to record

// Record value n times
hdr_record_values(
    histogram,  // Histogram to record to
    value,  // Value to record
    10)  // Record value 10 times

// Record value with correction for co-ordinated omission.
hdr_record_corrected_value(
    histogram,  // Histogram to record to
    value,  // Value to record
    1000)  // Record with expected interval of 1000.

// Print out the values of the histogram
hdr_percentiles_print(
    histogram,
    stdout,  // File to write to
    5,  // Granularity of printed values
    1.0,  // Multiplier for results
    CLASSIC);  // Format CLASSIC/CSV supported.

More examples

For more detailed examples of recording and logging results look at the hdr_decoder and hiccup examples. You can run hiccup and decoder and pipe the results of one into the other.

$ ./examples/hiccup | ./examples/hdr_decoder