On 11/13/2017 09:27 AM, Andreas Joseph Krogh wrote: > > In PG-10, with ICU enabled, is abbreviated keys now enabled? > Hello, I think yes : src/backend/utils/adt/varlena.c 1876 /* 1877 * Unfortunately, it seems that abbreviation for non-C collations is 1878 * broken on many common platforms; testing of multiple versions of glibc 1879 * reveals that, for many locales, strcoll() and strxfrm() do not return 1880 * consistent results, which is fatal to this optimization. While no 1881 * other libc other than Cygwin has so far been shown to have a problem, 1882 * we take the conservative course of action for right now and disable 1883 * this categorically. (Users who are certain this isn't a problem on 1884 * their system can define TRUST_STRXFRM.) 1885 * 1886 * Even apart from the risk of broken locales, it's possible that there 1887 * are platforms where the use of abbreviated keys should be disabled at 1888 * compile time. Having only 4 byte datums could make worst-case 1889 * performance drastically more likely, for example. Moreover, macOS's 1890 * strxfrm() implementation is known to not effectively concentrate a 1891 * significant amount of entropy from the original string in earlier 1892 * transformed blobs. It's possible that other supported platforms are 1893 * similarly encumbered. So, if we ever get past disabling this 1894 * categorically, we may still want or need to disable it for particular 1895 * platforms. 1896 */ 1897 #ifndef TRUST_STRXFRM 1898 if (!collate_c && !(locale && locale->provider == COLLPROVIDER_ICU)) 1899 abbreviate = false; 1900 #endif But I did not do any test to compare performances. Regards, -- Adrien NAYRAT http://dalibo.com - http://dalibo.org
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