oracle支持pipelined函数，可以在函数定义时指定RETURN 集合类型 PIPELINED 来说明当前函数是管道函数。
管道函数最大的作用就是可以使一次返回的集合类型，变为 逐条返回，大大减少内存的使用。
例如：嵌套表类型outrecset是函数f_trans的返回值，普通函数只能组装好嵌套表outrecset（全部缓存在内存），一次性返回。如果嵌套表内容较多，可能会占用较大的内存空间。
如果使用管道函数，可以通过pipe row(嵌套表中的一行)来代替return语句，函数把嵌套表逐行返回给上层处理，无需缓存，降低内存使用。
ORACLE实例：
CREATE OR REPLACE PACKAGE refcur_pkg AUTHID DEFINER IS
TYPE refcur_t IS REF CURSOR RETURN employees%ROWTYPE;
TYPE outrec_typ IS RECORD (
var_num NUMBER(6),
var_char1 VARCHAR2(30),
var_char2 VARCHAR2(30)
);
TYPE outrecset IS TABLE OF outrec_typ;
FUNCTION f_trans (p refcur_t) RETURN outrecset PIPELINED;
END refcur_pkg;
/
CREATE OR REPLACE PACKAGE BODY refcur_pkg IS
FUNCTION f_trans (p refcur_t) RETURN outrecset PIPELINED IS
out_rec outrec_typ;
in_rec p%ROWTYPE;
BEGIN
LOOP
FETCH p INTO in_rec; -- input row
EXIT WHEN p%NOTFOUND;
out_rec.var_num := in_rec.employee_id;
out_rec.var_char1 := in_rec.first_name;
out_rec.var_char2 := in_rec.last_name;
PIPE ROW(out_rec); -- first transformed output row
out_rec.var_char1 := in_rec.email;
out_rec.var_char2 := in_rec.phone_number;
PIPE ROW(out_rec); -- second transformed output row
END LOOP;
CLOSE p;
RETURN;
END f_trans;
END refcur_pkg;
/
SELECT * FROM TABLE (
refcur_pkg.f_trans (
CURSOR (SELECT * FROM employees WHERE department_id = 60)
)
);在PG中，普通的return语句也是需要一次性返回数据，但PG应该是参考ORACLE实现了return next的功能，也希望逐条返回数据（PG没有集合类型，已普通类型为例）：
drop function f1; create or replace function f1(in i int, out j int) returns setof int as $$ begin j := i+1; return next; j := i+2; return next; return; end$$ language plpgsql; select * from f1(42); j ---- 43 44
但在内核实现中，并不是逐条返回的，return next其实只起到了缓存数据的功能，总的数据集也是一次性返回SQL层的，和直接return没有区别（只有语法上的区别）。
所以PG的return setof函数并不能起到降低内存使用的效果。下面来分析具体过程。
return next目前支持三类数据的返回，var、rec、rows return next也可以不加参数，返回值按out参数列表拼接
static int
exec_stmt_return_next(PLpgSQL_execstate *estate,
PLpgSQL_stmt_return_next *stmt)
{
TupleDesc tupdesc;
int natts;
HeapTuple tuple;
MemoryContext oldcontext;初始化总结：
1 初始化的过程就是在构造Tuplestorestate，主要动作：
2 给estate->tuple_store_desc添加desc，desc来源：
#0 plpgsql_estate_setup (estate=0x7ffd81e2f850, func=0x2419028, rsi=0x7ffd81e2fb20, simple_eval_estate=0x0, simple_eval_resowner=0x0) at pl_exec.c:3972 #1 0x00007fe0a3992064 in plpgsql_exec_function (func=0x2419028, fcinfo=0x24da5a8, simple_eval_estate=0x0, simple_eval_resowner=0x0, procedure_resowner=0x0, atomic=true) at pl_exec.c:485 #2 0x00007fe0a39ac8f9 in plpgsql_call_handler (fcinfo=0x24da5a8) at pl_handler.c:277 #3 0x0000000000738829 in ExecMakeTableFunctionResult (setexpr=0x24e0b40, econtext=0x24e0a10, argContext=0x24da490, expectedDesc=0x24e1110, randomAccess=false) at execSRF.c:235 #4 0x0000000000753eed in FunctionNext (node=0x24e0800) at nodeFunctionscan.c:95 #5 0x000000000073a081 in ExecScanFetch (node=0x24e0800, accessMtd=0x753e3b <FunctionNext>, recheckMtd=0x754242 <FunctionRecheck>) at execScan.c:133 #6 0x000000000073a0f6 in ExecScan (node=0x24e0800, accessMtd=0x753e3b <FunctionNext>, recheckMtd=0x754242 <FunctionRecheck>) at execScan.c:182 #7 0x000000000075428c in ExecFunctionScan (pstate=0x24e0800) at nodeFunctionscan.c:270 #8 0x000000000073614e in ExecProcNodeFirst (node=0x24e0800) at execProcnode.c:464 #9 0x000000000072a08a in ExecProcNode (node=0x24e0800) at ../../../src/include/executor/executor.h:262 #10 0x000000000072cb80 in ExecutePlan (estate=0x24e05d8, planstate=0x24e0800, use_parallel_mode=false, operation=CMD_SELECT, sendTuples=true, numberTuples=0, direction=ForwardScanDirection, dest=0x24d5910, execute_once=true) at execMain.c:1632 #11 0x000000000072a6d1 in standard_ExecutorRun (queryDesc=0x23f1248, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:364 #12 0x000000000072a50b in ExecutorRun (queryDesc=0x23f1248, direction=ForwardScanDirection, count=0, execute_once=true) at execMain.c:308 #13 0x0000000000997ba9 in PortalRunSelect (portal=0x2474a28, forward=true, count=0, dest=0x24d5910) at pquery.c:924 #14 0x0000000000997867 in PortalRun (portal=0x2474a28, count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x24d5910, altdest=0x24d5910, qc=0x7ffd81e300b0) at pquery.c:768 #15 0x0000000000991408 in exec_simple_query (query_string=0x23c9518 "select * from f1(42);") at postgres.c:1238 #16 0x0000000000995a3e in PostgresMain (dbname=0x2400998 "postgres", username=0x23c5178 "mingjie") at postgres.c:4563 #17 0x00000000008d3cfe in BackendRun (port=0x23f7220) at postmaster.c:4396 #18 0x00000000008d3697 in BackendStartup (port=0x23f7220) at postmaster.c:4124 #19 0x00000000008d00b8 in ServerLoop () at postmaster.c:1791 #20 0x00000000008cf98a in PostmasterMain (argc=1, argv=0x23c3120) at postmaster.c:1463 #21 0x00000000007ada4b in main (argc=1, argv=0x23c3120) at main.c:200
分析：
if (estate->tuple_store == NULL)
exec_init_tuple_store(estate);
tupdesc = estate->tuple_store_desc;
natts = tupdesc->natts;
if (stmt->retvarno >= 0)
{
PLpgSQL_datum *retvar = estate->datums[stmt->retvarno];
switch (retvar->dtype)
{初始化函数exec_init_tuple_store
static void
exec_init_tuple_store(PLpgSQL_execstate *estate)
{
ReturnSetInfo *rsi = estate->rsi;
MemoryContext oldcxt;
ResourceOwner oldowner;
// 从"SPI Proc"切换到"ExecutorState"
oldcxt = MemoryContextSwitchTo(estate->tuple_store_cxt);
// 从“Portal”切换到"Portal"
oldowner = CurrentResourceOwner;
CurrentResourceOwner = estate->tuple_store_owner;
// 进入tuplestore_begin_heap函数
estate->tuple_store =
tuplestore_begin_heap(rsi->allowedModes & SFRM_Materialize_Random, false, work_mem);
CurrentResourceOwner = oldowner;
MemoryContextSwitchTo(oldcxt);
// 给estate添加DESC，rsi->expectedDesc的来源？
estate->tuple_store_desc = rsi->expectedDesc;
}进入tuplestore_begin_heap
Tuplestorestate *
tuplestore_begin_heap(bool randomAccess, bool interXact, int maxKBytes)
{
// 输入false不允许随机访问、false、8192
Tuplestorestate *state;
int eflags;
// eflags = EXEC_FLAG_REWIND
eflags = randomAccess ?
(EXEC_FLAG_BACKWARD | EXEC_FLAG_REWIND) :
(EXEC_FLAG_REWIND);
// 进入tuple store模块开始初始化返回Tuplestorestate，注意他会直接拿当前的memcontext
state = tuplestore_begin_common(eflags, interXact, maxKBytes);
// 返回的Tuplestorestate状态：
// state = {status = TSS_INMEM, eflags = 2, backward = false, interXact = false,
// truncated = false, availMem = 8372200, allowedMem = 8388608, tuples = 0,
// myfile = 0x0, context = "ExecutorState", resowner = "Portal", copytup = 0x0,
// writetup = 0x0, readtup = 0x0, memtuples = 0x24f0d88, memtupdeleted = 0,
// memtupcount = 0, memtupsize = 2048, growmemtuples = true, readptrs = 0x24e7a70,
// activeptr = 0, readptrcount = 1, readptrsize = 8, writepos_file = 0,writepos_offset = 0}
state->copytup = copytup_heap;
state->writetup = writetup_heap;
state->readtup = readtup_heap;
return state;
}后面根据返回值的不同，进入几个分支。
在进入前，desc已经获取到了： tupdesc = estate->tuple_store_desc; natts = tupdesc->natts;
case PLPGSQL_DTYPE_VAR:
{
PLpgSQL_var *var = (PLpgSQL_var *) retvar;
Datum retval = var->value;
bool isNull = var->isnull;
Form_pg_attribute attr = TupleDescAttr(tupdesc, 0);
if (natts != 1)
ereport(ERROR,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("wrong result type supplied in RETURN NEXT")));
// retval是一个eoh的头，后续处理需要一个1be的头（1be的data部分指向eoh）
retval = MakeExpandedObjectReadOnly(retval, isNull, var->datatype->typlen);
// 转成需要的类型
retval = exec_cast_value(estate,
retval,
&isNull,
var->datatype->typoid,
var->datatype->atttypmod,
attr->atttypid,
attr->atttypmod);
tuplestore_putvalues(estate->tuple_store, tupdesc, &retval, &isNull);
}
break;执行tuplestore_putvalues保存元组
void
tuplestore_putvalues(Tuplestorestate *state, TupleDesc tdesc,
Datum *values, bool *isnull)
{
MinimalTuple tuple;
MemoryContext oldcxt = MemoryContextSwitchTo(state->context);
tuple = heap_form_minimal_tuple(tdesc, values, isnull);
// 记录使用了多少空间，修改state->availMem
USEMEM(state, GetMemoryChunkSpace(tuple));
tuplestore_puttuple_common(state, (void *) tuple);
MemoryContextSwitchTo(oldcxt);
}
static void
tuplestore_puttuple_common(Tuplestorestate *state, void *tuple)
{
TSReadPointer *readptr;
int i;
ResourceOwner oldowner;
state->tuples++;
switch (state->status)
{内存态直接用数组缓存tuple，tuple使用的内存是在外层函数切换上下文申请的。
case TSS_INMEM:
readptr = state->readptrs;
for (i = 0; i < state->readptrcount; readptr++, i++)
{
if (readptr->eof_reached && i != state->activeptr)
{
readptr->eof_reached = false;
readptr->current = state->memtupcount;
}
}
if (state->memtupcount >= state->memtupsize - 1)
{
(void) grow_memtuples(state);
}
state->memtuples[state->memtupcount++] = tuple;
if (state->memtupcount < state->memtupsize && !LACKMEM(state))
return;
PrepareTempTablespaces();
oldowner = CurrentResourceOwner;
CurrentResourceOwner = state->resowner;
state->myfile = BufFileCreateTemp(state->interXact);
CurrentResourceOwner = oldowner;
state->backward = (state->eflags & EXEC_FLAG_BACKWARD) != 0;
state->status = TSS_WRITEFILE;
dumptuples(state);
break;
... case PLPGSQL_DTYPE_REC:
{
PLpgSQL_rec *rec = (PLpgSQL_rec *) retvar;
TupleDesc rec_tupdesc;
TupleConversionMap *tupmap;拿到record：
{dtype = PLPGSQL_DTYPE_REC, dno = 1, refname = 0x24db608 "r", lineno = 3, isconst = false, notnull = false, default_val = 0x0, datatype = {typname='foo'}, rectypeid = 17117, firstfield = -1, erh = 0x2509708}
if (rec->erh == NULL)
instantiate_empty_record_variable(estate, rec);
if (ExpandedRecordIsEmpty(rec->erh))
deconstruct_expanded_record(rec->erh);
// "SPI Proc"切到"ExprContext"
oldcontext = MemoryContextSwitchTo(get_eval_mcontext(estate));
// return erh->er_tupdesc;
rec_tupdesc = expanded_record_get_tupdesc(rec->erh);
// 从保存的desc：rec_tupdesc转换到输出的desc：tupdesc，第一步：生成转换map
tupmap = convert_tuples_by_position(rec_tupdesc,
tupdesc,
gettext_noop("wrong record type supplied in RETURN NEXT"));
tuple = expanded_record_get_tuple(rec->erh);
if (tupmap)
// 从保存的desc：rec_tupdesc转换到输出的desc：tupdesc，第二步：用map生成转换后的元组
tuple = execute_attr_map_tuple(tuple, tupmap);
// 缓存元组
tuplestore_puttuple(estate->tuple_store, tuple);
MemoryContextSwitchTo(oldcontext);
}
break;必须是两列以上的out参数，直接return next空，才会使用这段逻辑。
case PLPGSQL_DTYPE_ROW:
{
PLpgSQL_row *row = (PLpgSQL_row *) retvar;
oldcontext = MemoryContextSwitchTo(get_eval_mcontext(estate));
// 必须严格匹配tupdesc的类型，对不上则转换失败
tuple = make_tuple_from_row(estate, row, tupdesc);
if (tuple == NULL)
ereport(ERROR,...)
tuplestore_puttuple(estate->tuple_store, tuple);
MemoryContextSwitchTo(oldcontext);
}
break;
default:
elog(ERROR, "unrecognized dtype: %d", retvar->dtype);
break;
}
}drop function f1;
create or replace function f1(in i int, out j int) returns setof int as $$
begin
j := i+1;
return next;
j := i+2;
return next;
return;
end$$ language plpgsql;
select * from f1(42);
----
CREATE TABLE foo (fooid INT, foosubid INT, fooname TEXT);
INSERT INTO foo VALUES (1, 2, 'three');
INSERT INTO foo VALUES (4, 5, 'six');
CREATE OR REPLACE FUNCTION get_all_foo() RETURNS SETOF foo AS
$BODY$
DECLARE
r foo%rowtype;
BEGIN
FOR r IN
SELECT * FROM foo WHERE fooid > 0
LOOP
-- can do some processing here
RETURN NEXT r; -- return current row of SELECT
END LOOP;
RETURN;
END;
$BODY$
LANGUAGE plpgsql;
SELECT * FROM get_all_foo();
--------
drop function f1(int);
create function f1(in i int, out j int, out k text) returns setof record as $$
begin
j := i+1;
k := 'foo';
return next;
j := j+1;
k := 'foot';
return next;
return;
end$$ language plpgsql;
select * from f1(42);以上就是Postgresql源码分析returns setof函数oracle管道pipelined的详细内容，更多关于Postgresql returns setof函数的资料请关注脚本之家其它相关文章！
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