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robertmhaasrobertmhaas
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Introduce 64-bit hash functions with a 64-bit seed.
This will be useful for hash partitioning, which needs a way to seed the hash functions to avoid problems such as a hash index on a hash partitioned table clumping all values into a small portion of the bucket space; it's also useful for anything that wants a 64-bit hash value rather than a 32-bit hash value. Just in case somebody wants a 64-bit hash value that is compatible with the existing 32-bit hash values, make the low 32-bits of the 64-bit hash value match the 32-bit hash value when the seed is 0. Robert Haas and Amul Sul Discussion: http://postgr.es/m/CA+Tgmoafx2yoJuhCQQOL5CocEi-w_uG4S2xT0EtgiJnPGcHW3g@mail.gmail.com
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‎doc/src/sgml/xindex.sgml

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</table>
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<para>
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Hash indexes require one support function, shown in <xref
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Hash indexes require one support function, and allow a second one to be
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supplied at the operator class author's option, as shown in <xref
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linkend="xindex-hash-support-table">.
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</para>
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</thead>
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<tbody>
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<row>
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<entry>Compute the hash value for a key</entry>
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<entry>Compute the 32-bit hash value for a key</entry>
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<entry>1</entry>
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</row>
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<row>
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<entry>
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Compute the 64-bit hash value for a key given a 64-bit salt; if
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the salt is 0, the low 32 bits will match the value that would
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have been computed by function 1
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</entry>
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<entry>2</entry>
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</row>
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</tbody>
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</tgroup>
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</table>

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