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In array_agg(), don't create a new context for every group.

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Previously, each new array created a new memory context that started
out at 8kB. This is incredibly wasteful when there are lots of small
groups of just a few elements each.

Change initArrayResult() and friends to accept a "subcontext" argument
to indicate whether the caller wants the ArrayBuildState allocated in
a new subcontext or not. If not, it can no longer be released
separately from the rest of the memory context.

Fixes bug report by Frank van Vugt on 2013-10-19.

Tomas Vondra. Reviewed by Ali Akbar, Tom Lane, and me.
This commit is contained in:
Jeff Davis
2015-02-21 17:24:48 -08:00
parent e9fd5545de
commit b419865a81
6 changed files with 92 additions and 44 deletions
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106
src/backend/utils/adt/arrayfuncs.c
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@ -4650,6 +4650,7 @@ array_insert_slice(ArrayType *destArray,
*
* element_type is the array element type (must be a valid array element type)
* rcontext is where to keep working state
* subcontext is a flag determining whether to use a separate memory context
*
* Note: there are two common schemes for using accumArrayResult().
* In the older scheme, you start with a NULL ArrayBuildState pointer, and
@ -4659,24 +4660,39 @@ array_insert_slice(ArrayType *destArray,
* once per element. In this scheme you always end with a non-NULL pointer
* that you can pass to makeArrayResult; you get an empty array if there
* were no elements. This is preferred if an empty array is what you want.
*
* It's possible to choose whether to create a separate memory context for the
* array build state, or whether to allocate it directly within rcontext.
*
* When there are many concurrent small states (e.g. array_agg() using hash
* aggregation of many small groups), using a separate memory context for each
* one may result in severe memory bloat. In such cases, use the same memory
* context to initialize all such array build states, and pass
* subcontext=false.
*
* In cases when the array build states have different lifetimes, using a
* single memory context is impractical. Instead, pass subcontext=true so that
* the array build states can be freed individually.
*/
ArrayBuildState *
initArrayResult(Oid element_type, MemoryContext rcontext)
initArrayResult(Oid element_type, MemoryContext rcontext, bool subcontext)
{
ArrayBuildState *astate;
MemoryContext arr_context;
MemoryContext arr_context = rcontext;
/* Make a temporary context to hold all the junk */
arr_context = AllocSetContextCreate(rcontext,
"accumArrayResult",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
if (subcontext)
arr_context = AllocSetContextCreate(rcontext,
"accumArrayResult",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
astate = (ArrayBuildState *)
MemoryContextAlloc(arr_context, sizeof(ArrayBuildState));
astate->mcontext = arr_context;
astate->alen = 64; /* arbitrary starting array size */
astate->private_cxt = subcontext;
astate->alen = (subcontext ? 64 : 8); /* arbitrary starting array size */
astate->dvalues = (Datum *)
MemoryContextAlloc(arr_context, astate->alen * sizeof(Datum));
astate->dnulls = (bool *)
@ -4710,7 +4726,7 @@ accumArrayResult(ArrayBuildState *astate,
if (astate == NULL)
{
/* First time through --- initialize */
astate = initArrayResult(element_type, rcontext);
astate = initArrayResult(element_type, rcontext, true);
}
else
{
@ -4757,6 +4773,9 @@ accumArrayResult(ArrayBuildState *astate,
/*
* makeArrayResult - produce 1-D final result of accumArrayResult
*
* Note: only releases astate if it was initialized within a separate memory
* context (i.e. using subcontext=true when calling initArrayResult).
*
* astate is working state (must not be NULL)
* rcontext is where to construct result
*/
@ -4773,7 +4792,8 @@ makeArrayResult(ArrayBuildState *astate,
dims[0] = astate->nelems;
lbs[0] = 1;
return makeMdArrayResult(astate, ndims, dims, lbs, rcontext, true);
return makeMdArrayResult(astate, ndims, dims, lbs, rcontext,
astate->private_cxt);
}
/*
@ -4782,6 +4802,11 @@ makeArrayResult(ArrayBuildState *astate,
* beware: no check that specified dimensions match the number of values
* accumulated.
*
* Note: if the astate was not initialized within a separate memory context
* (that is, initArrayResult was called with subcontext=false), then using
* release=true is illegal. Instead, release astate along with the rest of its
* context when appropriate.
*
* astate is working state (must not be NULL)
* rcontext is where to construct result
* release is true if okay to release working state
@ -4814,7 +4839,10 @@ makeMdArrayResult(ArrayBuildState *astate,
/* Clean up all the junk */
if (release)
{
Assert(astate->private_cxt);
MemoryContextDelete(astate->mcontext);
}
return PointerGetDatum(result);
}
@ -4831,26 +4859,42 @@ makeMdArrayResult(ArrayBuildState *astate,
* initArrayResultArr - initialize an empty ArrayBuildStateArr
*
* array_type is the array type (must be a valid varlena array type)
* element_type is the type of the array's elements
* element_type is the type of the array's elements (lookup if InvalidOid)
* rcontext is where to keep working state
* subcontext is a flag determining whether to use a separate memory context
*/
ArrayBuildStateArr *
initArrayResultArr(Oid array_type, Oid element_type, MemoryContext rcontext)
initArrayResultArr(Oid array_type, Oid element_type, MemoryContext rcontext,
bool subcontext)
{
ArrayBuildStateArr *astate;
MemoryContext arr_context;
MemoryContext arr_context = rcontext; /* by default use the parent ctx */
/* Lookup element type, unless element_type already provided */
if (! OidIsValid(element_type))
{
element_type = get_element_type(array_type);
if (!OidIsValid(element_type))
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("data type %s is not an array type",
format_type_be(array_type))));
}
/* Make a temporary context to hold all the junk */
arr_context = AllocSetContextCreate(rcontext,
"accumArrayResultArr",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
if (subcontext)
arr_context = AllocSetContextCreate(rcontext,
"accumArrayResultArr",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
/* Note we initialize all fields to zero */
astate = (ArrayBuildStateArr *)
MemoryContextAllocZero(arr_context, sizeof(ArrayBuildStateArr));
astate->mcontext = arr_context;
astate->private_cxt = subcontext;
/* Save relevant datatype information */
astate->array_type = array_type;
@ -4897,21 +4941,9 @@ accumArrayResultArr(ArrayBuildStateArr *astate,
arg = DatumGetArrayTypeP(dvalue);
if (astate == NULL)
{
/* First time through --- initialize */
Oid element_type = get_element_type(array_type);
if (!OidIsValid(element_type))
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("data type %s is not an array type",
format_type_be(array_type))));
astate = initArrayResultArr(array_type, element_type, rcontext);
}
astate = initArrayResultArr(array_type, InvalidOid, rcontext, true);
else
{
Assert(astate->array_type == array_type);
}
oldcontext = MemoryContextSwitchTo(astate->mcontext);
@ -5090,7 +5122,10 @@ makeArrayResultArr(ArrayBuildStateArr *astate,
/* Clean up all the junk */
if (release)
{
Assert(astate->private_cxt);
MemoryContextDelete(astate->mcontext);
}
return PointerGetDatum(result);
}
@ -5106,9 +5141,10 @@ makeArrayResultArr(ArrayBuildStateArr *astate,
*
* input_type is the input datatype (either element or array type)
* rcontext is where to keep working state
* subcontext is a flag determining whether to use a separate memory context
*/
ArrayBuildStateAny *
initArrayResultAny(Oid input_type, MemoryContext rcontext)
initArrayResultAny(Oid input_type, MemoryContext rcontext, bool subcontext)
{
ArrayBuildStateAny *astate;
Oid element_type = get_element_type(input_type);
@ -5118,7 +5154,7 @@ initArrayResultAny(Oid input_type, MemoryContext rcontext)
/* Array case */
ArrayBuildStateArr *arraystate;
arraystate = initArrayResultArr(input_type, element_type, rcontext);
arraystate = initArrayResultArr(input_type, InvalidOid, rcontext, subcontext);
astate = (ArrayBuildStateAny *)
MemoryContextAlloc(arraystate->mcontext,
sizeof(ArrayBuildStateAny));
@ -5133,7 +5169,7 @@ initArrayResultAny(Oid input_type, MemoryContext rcontext)
/* Let's just check that we have a type that can be put into arrays */
Assert(OidIsValid(get_array_type(input_type)));
scalarstate = initArrayResult(input_type, rcontext);
scalarstate = initArrayResult(input_type, rcontext, subcontext);
astate = (ArrayBuildStateAny *)
MemoryContextAlloc(scalarstate->mcontext,
sizeof(ArrayBuildStateAny));
@ -5159,7 +5195,7 @@ accumArrayResultAny(ArrayBuildStateAny *astate,
MemoryContext rcontext)
{
if (astate == NULL)
astate = initArrayResultAny(input_type, rcontext);
astate = initArrayResultAny(input_type, rcontext, true);
if (astate->scalarstate)
(void) accumArrayResult(astate->scalarstate,