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Support multi-stage aggregation.

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Aggregate nodes now have two new modes: a "partial" mode where they
output the unfinalized transition state, and a "finalize" mode where
they accept unfinalized transition states rather than individual
values as input.

These new modes are not used anywhere yet, but they will be necessary
for parallel aggregation.  The infrastructure also figures to be
useful for cases where we want to aggregate local data and remote
data via the FDW interface, and want to bring back partial aggregates
from the remote side that can then be combined with locally generated
partial aggregates to produce the final value.  It may also be useful
even when neither FDWs nor parallelism are in play, as explained in
the comments in nodeAgg.c.

David Rowley and Simon Riggs, reviewed by KaiGai Kohei, Heikki
Linnakangas, Haribabu Kommi, and me.
This commit is contained in:
Robert Haas
2016-01-20 13:46:50 -05:00
parent c8642d909f
commit a7de3dc5c3
21 changed files with 652 additions and 234 deletions
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16
doc/src/sgml/ref/create_aggregate.sgml
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@@ -27,6 +27,7 @@ CREATE AGGREGATE <replaceable class="parameter">name</replaceable> ( [ <replacea
[ , SSPACE = <replaceable class="PARAMETER">state_data_size</replaceable> ]
[ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ]
[ , FINALFUNC_EXTRA ]
[ , COMBINEFUNC = <replaceable class="PARAMETER">combinefunc</replaceable> ]
[ , INITCOND = <replaceable class="PARAMETER">initial_condition</replaceable> ]
[ , MSFUNC = <replaceable class="PARAMETER">msfunc</replaceable> ]
[ , MINVFUNC = <replaceable class="PARAMETER">minvfunc</replaceable> ]
@@ -45,6 +46,7 @@ CREATE AGGREGATE <replaceable class="parameter">name</replaceable> ( [ [ <replac
[ , SSPACE = <replaceable class="PARAMETER">state_data_size</replaceable> ]
[ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ]
[ , FINALFUNC_EXTRA ]
[ , COMBINEFUNC = <replaceable class="PARAMETER">combinefunc</replaceable> ]
[ , INITCOND = <replaceable class="PARAMETER">initial_condition</replaceable> ]
[ , HYPOTHETICAL ]
)
@@ -58,6 +60,7 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
[ , SSPACE = <replaceable class="PARAMETER">state_data_size</replaceable> ]
[ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ]
[ , FINALFUNC_EXTRA ]
[ , COMBINEFUNC = <replaceable class="PARAMETER">combinefunc</replaceable> ]
[ , INITCOND = <replaceable class="PARAMETER">initial_condition</replaceable> ]
[ , MSFUNC = <replaceable class="PARAMETER">msfunc</replaceable> ]
[ , MINVFUNC = <replaceable class="PARAMETER">minvfunc</replaceable> ]
@@ -105,12 +108,15 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
functions:
a state transition function
<replaceable class="PARAMETER">sfunc</replaceable>,
and an optional final calculation function
<replaceable class="PARAMETER">ffunc</replaceable>.
an optional final calculation function
<replaceable class="PARAMETER">ffunc</replaceable>,
and an optional combine function
<replaceable class="PARAMETER">combinefunc</replaceable>.
These are used as follows:
<programlisting>
<replaceable class="PARAMETER">sfunc</replaceable>( internal-state, next-data-values ) ---> next-internal-state
<replaceable class="PARAMETER">ffunc</replaceable>( internal-state ) ---> aggregate-value
<replaceable class="PARAMETER">combinefunc</replaceable>( internal-state, internal-state ) ---> next-internal-state
</programlisting>
</para>
@@ -127,6 +133,12 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
is returned as-is.
</para>
<para>
An aggregate function may also supply a combining function, which allows
the aggregation process to be broken down into multiple steps. This
facilitates query optimization techniques such as parallel query.
</para>
<para>
An aggregate function can provide an initial condition,
that is, an initial value for the internal state value.