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/*-------------------------------------------------------------------------
*
* tuplestore.c
* Generalized routines for temporary tuple storage.
*
* This module handles temporary storage of tuples for purposes such
* as Materialize nodes, hashjoin batch files, etc. It is essentially
* a dumbed-down version of tuplesort.c; it does no sorting of tuples
* but can only store and regurgitate a sequence of tuples. However,
* because no sort is required, it is allowed to start reading the sequence
* before it has all been written. This is particularly useful for cursors,
* because it allows random access within the already-scanned portion of
* a query without having to process the underlying scan to completion.
* Also, it is possible to support multiple independent read pointers.
*
* A temporary file is used to handle the data if it exceeds the
* space limit specified by the caller.
*
* The (approximate) amount of memory allowed to the tuplestore is specified
* in kilobytes by the caller. We absorb tuples and simply store them in an
* in-memory array as long as we haven't exceeded maxKBytes. If we do exceed
* maxKBytes, we dump all the tuples into a temp file and then read from that
* when needed.
*
* Upon creation, a tuplestore supports a single read pointer, numbered 0.
* Additional read pointers can be created using tuplestore_alloc_read_pointer.
* Mark/restore behavior is supported by copying read pointers.
*
* When the caller requests backward-scan capability, we write the temp file
* in a format that allows either forward or backward scan. Otherwise, only
* forward scan is allowed. A request for backward scan must be made before
* putting any tuples into the tuplestore. Rewind is normally allowed but
* can be turned off via tuplestore_set_eflags; turning off rewind for all
* read pointers enables truncation of the tuplestore at the oldest read point
* for minimal memory usage. (The caller must explicitly call tuplestore_trim
* at appropriate times for truncation to actually happen.)
*
* Note: in TSS_WRITEFILE state, the temp file's seek position is the
* current write position, and the write-position variables in the tuplestore
* aren't kept up to date. Similarly, in TSS_READFILE state the temp file's
* seek position is the active read pointer's position, and that read pointer
* isn't kept up to date. We update the appropriate variables using ftell()
* before switching to the other state or activating a different read pointer.
*
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/utils/sort/tuplestore.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <limits.h>
#include "access/htup_details.h"
#include "commands/tablespace.h"
#include "executor/executor.h"
#include "miscadmin.h"
#include "storage/buffile.h"
#include "utils/memutils.h"
#include "utils/resowner.h"
/*
* Possible states of a Tuplestore object. These denote the states that
* persist between calls of Tuplestore routines.
*/
typedef enum
{
TSS_INMEM, /* Tuples still fit in memory */
TSS_WRITEFILE, /* Writing to temp file */
TSS_READFILE /* Reading from temp file */
} TupStoreStatus;
/*
* State for a single read pointer. If we are in state INMEM then all the
* read pointers' "current" fields denote the read positions. In state
* WRITEFILE, the file/offset fields denote the read positions. In state
* READFILE, inactive read pointers have valid file/offset, but the active
* read pointer implicitly has position equal to the temp file's seek position.
*
* Special case: if eof_reached is true, then the pointer's read position is
* implicitly equal to the write position, and current/file/offset aren't
* maintained. This way we need not update all the read pointers each time
* we write.
*/
typedef struct
{
int eflags; /* capability flags */
bool eof_reached; /* read has reached EOF */
int current; /* next array index to read */
int file; /* temp file# */
off_t offset; /* byte offset in file */
} TSReadPointer;
/*
* Private state of a Tuplestore operation.
*/
struct Tuplestorestate
{
TupStoreStatus status; /* enumerated value as shown above */
int eflags; /* capability flags (OR of pointers' flags) */
bool backward; /* store extra length words in file? */
bool interXact; /* keep open through transactions? */
bool truncated; /* tuplestore_trim has removed tuples? */
int64 availMem; /* remaining memory available, in bytes */
int64 allowedMem; /* total memory allowed, in bytes */
int64 tuples; /* number of tuples added */
BufFile *myfile; /* underlying file, or NULL if none */
MemoryContext context; /* memory context for holding tuples */
ResourceOwner resowner; /* resowner for holding temp files */
/*
* These function pointers decouple the routines that must know what kind
* of tuple we are handling from the routines that don't need to know it.
* They are set up by the tuplestore_begin_xxx routines.
*
* (Although tuplestore.c currently only supports heap tuples, I've copied
* this part of tuplesort.c so that extension to other kinds of objects
* will be easy if it's ever needed.)
*
* Function to copy a supplied input tuple into palloc'd space. (NB: we
* assume that a single pfree() is enough to release the tuple later, so
* the representation must be "flat" in one palloc chunk.) state->availMem
* must be decreased by the amount of space used.
*/
void *(*copytup) (Tuplestorestate *state, void *tup);
/*
* Function to write a stored tuple onto tape. The representation of the
* tuple on tape need not be the same as it is in memory; requirements on
* the tape representation are given below. After writing the tuple,
* pfree() it, and increase state->availMem by the amount of memory space
* thereby released.
*/
void (*writetup) (Tuplestorestate *state, void *tup);
/*
* Function to read a stored tuple from tape back into memory. 'len' is
* the already-read length of the stored tuple. Create and return a
* palloc'd copy, and decrease state->availMem by the amount of memory
* space consumed.
*/
void *(*readtup) (Tuplestorestate *state, unsigned int len);
/*
* This array holds pointers to tuples in memory if we are in state INMEM.
* In states WRITEFILE and READFILE it's not used.
*
* When memtupdeleted > 0, the first memtupdeleted pointers are already
* released due to a tuplestore_trim() operation, but we haven't expended
* the effort to slide the remaining pointers down. These unused pointers
* are set to NULL to catch any invalid accesses. Note that memtupcount
* includes the deleted pointers.
*/
void **memtuples; /* array of pointers to palloc'd tuples */
int memtupdeleted; /* the first N slots are currently unused */
int memtupcount; /* number of tuples currently present */
int memtupsize; /* allocated length of memtuples array */
bool growmemtuples; /* memtuples' growth still underway? */
/*
* These variables are used to keep track of the current positions.
*
* In state WRITEFILE, the current file seek position is the write point;
* in state READFILE, the write position is remembered in writepos_xxx.
* (The write position is the same as EOF, but since BufFileSeek doesn't
* currently implement SEEK_END, we have to remember it explicitly.)
*/
TSReadPointer *readptrs; /* array of read pointers */
int activeptr; /* index of the active read pointer */
int readptrcount; /* number of pointers currently valid */
int readptrsize; /* allocated length of readptrs array */
int writepos_file; /* file# (valid if READFILE state) */
off_t writepos_offset; /* offset (valid if READFILE state) */
};
#define COPYTUP(state,tup) ((*(state)->copytup) (state, tup))
#define WRITETUP(state,tup) ((*(state)->writetup) (state, tup))
#define READTUP(state,len) ((*(state)->readtup) (state, len))
#define LACKMEM(state) ((state)->availMem < 0)
#define USEMEM(state,amt) ((state)->availMem -= (amt))
#define FREEMEM(state,amt) ((state)->availMem += (amt))
/*--------------------
*
* NOTES about on-tape representation of tuples:
*
* We require the first "unsigned int" of a stored tuple to be the total size
* on-tape of the tuple, including itself (so it is never zero).
* The remainder of the stored tuple
* may or may not match the in-memory representation of the tuple ---
* any conversion needed is the job of the writetup and readtup routines.
*
* If state->backward is true, then the stored representation of
* the tuple must be followed by another "unsigned int" that is a copy of the
* length --- so the total tape space used is actually sizeof(unsigned int)
* more than the stored length value. This allows read-backwards. When
* state->backward is not set, the write/read routines may omit the extra
* length word.
*
* writetup is expected to write both length words as well as the tuple
* data. When readtup is called, the tape is positioned just after the
* front length word; readtup must read the tuple data and advance past
* the back length word (if present).
*
* The write/read routines can make use of the tuple description data
* stored in the Tuplestorestate record, if needed. They are also expected
* to adjust state->availMem by the amount of memory space (not tape space!)
* released or consumed. There is no error return from either writetup
* or readtup; they should ereport() on failure.
*
*
* NOTES about memory consumption calculations:
*
* We count space allocated for tuples against the maxKBytes limit,
* plus the space used by the variable-size array memtuples.
* Fixed-size space (primarily the BufFile I/O buffer) is not counted.
* We don't worry about the size of the read pointer array, either.
*
* Note that we count actual space used (as shown by GetMemoryChunkSpace)
* rather than the originally-requested size. This is important since
* palloc can add substantial overhead. It's not a complete answer since
* we won't count any wasted space in palloc allocation blocks, but it's
* a lot better than what we were doing before 7.3.
*
*--------------------
*/
static Tuplestorestate *tuplestore_begin_common(int eflags,
bool interXact,
int maxKBytes);
static void tuplestore_puttuple_common(Tuplestorestate *state, void *tuple);
static void dumptuples(Tuplestorestate *state);
static unsigned int getlen(Tuplestorestate *state, bool eofOK);
static void *copytup_heap(Tuplestorestate *state, void *tup);
static void writetup_heap(Tuplestorestate *state, void *tup);
static void *readtup_heap(Tuplestorestate *state, unsigned int len);
/*
* tuplestore_begin_xxx
*
* Initialize for a tuple store operation.
*/
static Tuplestorestate *
tuplestore_begin_common(int eflags, bool interXact, int maxKBytes)
{
Tuplestorestate *state;
state = (Tuplestorestate *) palloc0(sizeof(Tuplestorestate));
state->status = TSS_INMEM;
state->eflags = eflags;
state->interXact = interXact;
state->truncated = false;
state->allowedMem = maxKBytes * 1024L;
state->availMem = state->allowedMem;
state->myfile = NULL;
state->context = CurrentMemoryContext;
state->resowner = CurrentResourceOwner;
state->memtupdeleted = 0;
state->memtupcount = 0;
state->tuples = 0;
/*
* Initial size of array must be more than ALLOCSET_SEPARATE_THRESHOLD;
* see comments in grow_memtuples().
*/
state->memtupsize = Max(16384 / sizeof(void *),
ALLOCSET_SEPARATE_THRESHOLD / sizeof(void *) + 1);
state->growmemtuples = true;
state->memtuples = (void **) palloc(state->memtupsize * sizeof(void *));
USEMEM(state, GetMemoryChunkSpace(state->memtuples));
state->activeptr = 0;
state->readptrcount = 1;
state->readptrsize = 8; /* arbitrary */
state->readptrs = (TSReadPointer *)
palloc(state->readptrsize * sizeof(TSReadPointer));
state->readptrs[0].eflags = eflags;
state->readptrs[0].eof_reached = false;
state->readptrs[0].current = 0;
return state;
}
/*
* tuplestore_begin_heap
*
* Create a new tuplestore; other types of tuple stores (other than
* "heap" tuple stores, for heap tuples) are possible, but not presently
* implemented.
*
* randomAccess: if true, both forward and backward accesses to the
* tuple store are allowed.
*
* interXact: if true, the files used for on-disk storage persist beyond the
* end of the current transaction. NOTE: It's the caller's responsibility to
* create such a tuplestore in a memory context and resource owner that will
* also survive transaction boundaries, and to ensure the tuplestore is closed
* when it's no longer wanted.
*
* maxKBytes: how much data to store in memory (any data beyond this
* amount is paged to disk). When in doubt, use work_mem.
*/
Tuplestorestate *
tuplestore_begin_heap(bool randomAccess, bool interXact, int maxKBytes)
{
Tuplestorestate *state;
int eflags;
/*
* This interpretation of the meaning of randomAccess is compatible with
* the pre-8.3 behavior of tuplestores.
*/
eflags = randomAccess ?
(EXEC_FLAG_BACKWARD | EXEC_FLAG_REWIND) :
(EXEC_FLAG_REWIND);
state = tuplestore_begin_common(eflags, interXact, maxKBytes);
state->copytup = copytup_heap;
state->writetup = writetup_heap;
state->readtup = readtup_heap;
return state;
}
/*
* tuplestore_set_eflags
*
* Set the capability flags for read pointer 0 at a finer grain than is
* allowed by tuplestore_begin_xxx. This must be called before inserting
* any data into the tuplestore.
*
* eflags is a bitmask following the meanings used for executor node
* startup flags (see executor.h). tuplestore pays attention to these bits:
* EXEC_FLAG_REWIND need rewind to start
* EXEC_FLAG_BACKWARD need backward fetch
* If tuplestore_set_eflags is not called, REWIND is allowed, and BACKWARD
* is set per "randomAccess" in the tuplestore_begin_xxx call.
*
* NOTE: setting BACKWARD without REWIND means the pointer can read backwards,
* but not further than the truncation point (the furthest-back read pointer
* position at the time of the last tuplestore_trim call).
*/
void
tuplestore_set_eflags(Tuplestorestate *state, int eflags)
{
int i;
if (state->status != TSS_INMEM || state->memtupcount != 0)
elog(ERROR, "too late to call tuplestore_set_eflags");
state->readptrs[0].eflags = eflags;
for (i = 1; i < state->readptrcount; i++)
eflags |= state->readptrs[i].eflags;
state->eflags = eflags;
}
/*
* tuplestore_alloc_read_pointer - allocate another read pointer.
*
* Returns the pointer's index.
*
* The new pointer initially copies the position of read pointer 0.
* It can have its own eflags, but if any data has been inserted into
* the tuplestore, these eflags must not represent an increase in
* requirements.
*/
int
tuplestore_alloc_read_pointer(Tuplestorestate *state, int eflags)
{
/* Check for possible increase of requirements */
if (state->status != TSS_INMEM || state->memtupcount != 0)
{
if ((state->eflags | eflags) != state->eflags)
elog(ERROR, "too late to require new tuplestore eflags");
}
/* Make room for another read pointer if needed */
if (state->readptrcount >= state->readptrsize)
{
int newcnt = state->readptrsize * 2;
state->readptrs = (TSReadPointer *)
repalloc(state->readptrs, newcnt * sizeof(TSReadPointer));
state->readptrsize = newcnt;
}
/* And set it up */
state->readptrs[state->readptrcount] = state->readptrs[0];
state->readptrs[state->readptrcount].eflags = eflags;
state->eflags |= eflags;
return state->readptrcount++;
}
/*
* tuplestore_clear
*
* Delete all the contents of a tuplestore, and reset its read pointers
* to the start.
*/
void
tuplestore_clear(Tuplestorestate *state)
{
int i;
TSReadPointer *readptr;
if (state->myfile)
BufFileClose(state->myfile);
state->myfile = NULL;
if (state->memtuples)
{
for (i = state->memtupdeleted; i < state->memtupcount; i++)
{
FREEMEM(state, GetMemoryChunkSpace(state->memtuples[i]));
pfree(state->memtuples[i]);
}
}
state->status = TSS_INMEM;
state->truncated = false;
state->memtupdeleted = 0;
state->memtupcount = 0;
state->tuples = 0;
readptr = state->readptrs;
for (i = 0; i < state->readptrcount; readptr++, i++)
{
readptr->eof_reached = false;
readptr->current = 0;
}
}
/*
* tuplestore_end
*
* Release resources and clean up.
*/
void
tuplestore_end(Tuplestorestate *state)
{
int i;
if (state->myfile)
BufFileClose(state->myfile);
if (state->memtuples)
{
for (i = state->memtupdeleted; i < state->memtupcount; i++)
pfree(state->memtuples[i]);
pfree(state->memtuples);
}
pfree(state->readptrs);
pfree(state);
}
/*
* tuplestore_select_read_pointer - make the specified read pointer active
*/
void
tuplestore_select_read_pointer(Tuplestorestate *state, int ptr)
{
TSReadPointer *readptr;
TSReadPointer *oldptr;
Assert(ptr >= 0 && ptr < state->readptrcount);
/* No work if already active */
if (ptr == state->activeptr)
return;
readptr = &state->readptrs[ptr];
oldptr = &state->readptrs[state->activeptr];
switch (state->status)
{
case TSS_INMEM:
case TSS_WRITEFILE:
/* no work */
break;
case TSS_READFILE:
/*
* First, save the current read position in the pointer about to
* become inactive.
*/
if (!oldptr->eof_reached)
BufFileTell(state->myfile,
&oldptr->file,
&oldptr->offset);
/*
* We have to make the temp file's seek position equal to the
* logical position of the new read pointer. In eof_reached
* state, that's the EOF, which we have available from the saved
* write position.
*/
if (readptr->eof_reached)
{
if (BufFileSeek(state->myfile,
state->writepos_file,
state->writepos_offset,
SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
}
else
{
if (BufFileSeek(state->myfile,
readptr->file,
readptr->offset,
SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
}
break;
default:
elog(ERROR, "invalid tuplestore state");
break;
}
state->activeptr = ptr;
}
/*
* tuplestore_tuple_count
*
* Returns the number of tuples added since creation or the last
* tuplestore_clear().
*/
int64
tuplestore_tuple_count(Tuplestorestate *state)
{
return state->tuples;
}
/*
* tuplestore_ateof
*
* Returns the active read pointer's eof_reached state.
*/
bool
tuplestore_ateof(Tuplestorestate *state)
{
return state->readptrs[state->activeptr].eof_reached;
}
/*
* Grow the memtuples[] array, if possible within our memory constraint. We
* must not exceed INT_MAX tuples in memory or the caller-provided memory
* limit. Return true if we were able to enlarge the array, false if not.
*
* Normally, at each increment we double the size of the array. When doing
* that would exceed a limit, we attempt one last, smaller increase (and then
* clear the growmemtuples flag so we don't try any more). That allows us to
* use memory as fully as permitted; sticking to the pure doubling rule could
* result in almost half going unused. Because availMem moves around with
* tuple addition/removal, we need some rule to prevent making repeated small
* increases in memtupsize, which would just be useless thrashing. The
* growmemtuples flag accomplishes that and also prevents useless
* recalculations in this function.
*/
static bool
grow_memtuples(Tuplestorestate *state)
{
int newmemtupsize;
int memtupsize = state->memtupsize;
int64 memNowUsed = state->allowedMem - state->availMem;
/* Forget it if we've already maxed out memtuples, per comment above */
if (!state->growmemtuples)
return false;
/* Select new value of memtupsize */
if (memNowUsed <= state->availMem)
{
/*
* We've used no more than half of allowedMem; double our usage,
* clamping at INT_MAX tuples.
*/
if (memtupsize < INT_MAX / 2)
newmemtupsize = memtupsize * 2;
else
{
newmemtupsize = INT_MAX;
state->growmemtuples = false;
}
}
else
{
/*
* This will be the last increment of memtupsize. Abandon doubling
* strategy and instead increase as much as we safely can.
*
* To stay within allowedMem, we can't increase memtupsize by more
* than availMem / sizeof(void *) elements. In practice, we want to
* increase it by considerably less, because we need to leave some
* space for the tuples to which the new array slots will refer. We
* assume the new tuples will be about the same size as the tuples
* we've already seen, and thus we can extrapolate from the space
* consumption so far to estimate an appropriate new size for the
* memtuples array. The optimal value might be higher or lower than
* this estimate, but it's hard to know that in advance. We again
* clamp at INT_MAX tuples.
*
* This calculation is safe against enlarging the array so much that
* LACKMEM becomes true, because the memory currently used includes
* the present array; thus, there would be enough allowedMem for the
* new array elements even if no other memory were currently used.
*
* We do the arithmetic in float8, because otherwise the product of
* memtupsize and allowedMem could overflow. Any inaccuracy in the
* result should be insignificant; but even if we computed a
* completely insane result, the checks below will prevent anything
* really bad from happening.
*/
double grow_ratio;
grow_ratio = (double) state->allowedMem / (double) memNowUsed;
if (memtupsize * grow_ratio < INT_MAX)
newmemtupsize = (int) (memtupsize * grow_ratio);
else
newmemtupsize = INT_MAX;
/* We won't make any further enlargement attempts */
state->growmemtuples = false;
}
/* Must enlarge array by at least one element, else report failure */
if (newmemtupsize <= memtupsize)
goto noalloc;
/*
* On a 32-bit machine, allowedMem could exceed MaxAllocHugeSize. Clamp
* to ensure our request won't be rejected. Note that we can easily
* exhaust address space before facing this outcome. (This is presently
* impossible due to guc.c's MAX_KILOBYTES limitation on work_mem, but
* don't rely on that at this distance.)
*/
if ((Size) newmemtupsize >= MaxAllocHugeSize / sizeof(void *))
{
newmemtupsize = (int) (MaxAllocHugeSize / sizeof(void *));
state->growmemtuples = false; /* can't grow any more */
}
/*
* We need to be sure that we do not cause LACKMEM to become true, else
* the space management algorithm will go nuts. The code above should
* never generate a dangerous request, but to be safe, check explicitly
* that the array growth fits within availMem. (We could still cause
* LACKMEM if the memory chunk overhead associated with the memtuples
* array were to increase. That shouldn't happen because we chose the
* initial array size large enough to ensure that palloc will be treating
* both old and new arrays as separate chunks. But we'll check LACKMEM
* explicitly below just in case.)
*/
if (state->availMem < (int64) ((newmemtupsize - memtupsize) * sizeof(void *)))
goto noalloc;
/* OK, do it */
FREEMEM(state, GetMemoryChunkSpace(state->memtuples));
state->memtupsize = newmemtupsize;
state->memtuples = (void **)
repalloc_huge(state->memtuples,
state->memtupsize * sizeof(void *));
USEMEM(state, GetMemoryChunkSpace(state->memtuples));
if (LACKMEM(state))
elog(ERROR, "unexpected out-of-memory situation in tuplestore");
return true;
noalloc:
/* If for any reason we didn't realloc, shut off future attempts */
state->growmemtuples = false;
return false;
}
/*
* Accept one tuple and append it to the tuplestore.
*
* Note that the input tuple is always copied; the caller need not save it.
*
* If the active read pointer is currently "at EOF", it remains so (the read
* pointer implicitly advances along with the write pointer); otherwise the
* read pointer is unchanged. Non-active read pointers do not move, which
* means they are certain to not be "at EOF" immediately after puttuple.
* This curious-seeming behavior is for the convenience of nodeMaterial.c and
* nodeCtescan.c, which would otherwise need to do extra pointer repositioning
* steps.
*
* tuplestore_puttupleslot() is a convenience routine to collect data from
* a TupleTableSlot without an extra copy operation.
*/
void
tuplestore_puttupleslot(Tuplestorestate *state,
TupleTableSlot *slot)
{
MinimalTuple tuple;
MemoryContext oldcxt = MemoryContextSwitchTo(state->context);
/*
* Form a MinimalTuple in working memory
*/
tuple = ExecCopySlotMinimalTuple(slot);
USEMEM(state, GetMemoryChunkSpace(tuple));
tuplestore_puttuple_common(state, (void *) tuple);
MemoryContextSwitchTo(oldcxt);
}
/*
* "Standard" case to copy from a HeapTuple. This is actually now somewhat
* deprecated, but not worth getting rid of in view of the number of callers.
*/
void
tuplestore_puttuple(Tuplestorestate *state, HeapTuple tuple)
{
MemoryContext oldcxt = MemoryContextSwitchTo(state->context);
/*
* Copy the tuple. (Must do this even in WRITEFILE case. Note that
* COPYTUP includes USEMEM, so we needn't do that here.)
*/
tuple = COPYTUP(state, tuple);
tuplestore_puttuple_common(state, (void *) tuple);
MemoryContextSwitchTo(oldcxt);
}
/*
* Similar to tuplestore_puttuple(), but work from values + nulls arrays.
* This avoids an extra tuple-construction operation.
*/
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);
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)
{
case TSS_INMEM:
/*
* Update read pointers as needed; see API spec above.
*/
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;
}
}
/*
* Grow the array as needed. Note that we try to grow the array
* when there is still one free slot remaining --- if we fail,
* there'll still be room to store the incoming tuple, and then
* we'll switch to tape-based operation.
*/
if (state->memtupcount >= state->memtupsize - 1)
{
(void) grow_memtuples(state);
Assert(state->memtupcount < state->memtupsize);
}
/* Stash the tuple in the in-memory array */
state->memtuples[state->memtupcount++] = tuple;
/*
* Done if we still fit in available memory and have array slots.
*/
if (state->memtupcount < state->memtupsize && !LACKMEM(state))
return;
/*
* Nope; time to switch to tape-based operation. Make sure that
* the temp file(s) are created in suitable temp tablespaces.
*/
PrepareTempTablespaces();
/* associate the file with the store's resource owner */
oldowner = CurrentResourceOwner;
CurrentResourceOwner = state->resowner;
state->myfile = BufFileCreateTemp(state->interXact);
CurrentResourceOwner = oldowner;
/*
* Freeze the decision about whether trailing length words will be
* used. We can't change this choice once data is on tape, even
* though callers might drop the requirement.
*/
state->backward = (state->eflags & EXEC_FLAG_BACKWARD) != 0;
state->status = TSS_WRITEFILE;
dumptuples(state);
break;
case TSS_WRITEFILE:
/*
* Update read pointers as needed; see API spec above. Note:
* BufFileTell is quite cheap, so not worth trying to avoid
* multiple calls.
*/
readptr = state->readptrs;
for (i = 0; i < state->readptrcount; readptr++, i++)
{
if (readptr->eof_reached && i != state->activeptr)
{
readptr->eof_reached = false;
BufFileTell(state->myfile,
&readptr->file,
&readptr->offset);
}
}
WRITETUP(state, tuple);
break;
case TSS_READFILE:
/*
* Switch from reading to writing.
*/
if (!state->readptrs[state->activeptr].eof_reached)
BufFileTell(state->myfile,
&state->readptrs[state->activeptr].file,
&state->readptrs[state->activeptr].offset);
if (BufFileSeek(state->myfile,
state->writepos_file, state->writepos_offset,
SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
state->status = TSS_WRITEFILE;
/*
* Update read pointers as needed; see API spec above.
*/
readptr = state->readptrs;
for (i = 0; i < state->readptrcount; readptr++, i++)
{
if (readptr->eof_reached && i != state->activeptr)
{
readptr->eof_reached = false;
readptr->file = state->writepos_file;
readptr->offset = state->writepos_offset;
}
}
WRITETUP(state, tuple);
break;
default:
elog(ERROR, "invalid tuplestore state");
break;
}
}
/*
* Fetch the next tuple in either forward or back direction.
* Returns NULL if no more tuples. If should_free is set, the
* caller must pfree the returned tuple when done with it.
*
* Backward scan is only allowed if randomAccess was set true or
* EXEC_FLAG_BACKWARD was specified to tuplestore_set_eflags().
*/
static void *
tuplestore_gettuple(Tuplestorestate *state, bool forward,
bool *should_free)
{
TSReadPointer *readptr = &state->readptrs[state->activeptr];
unsigned int tuplen;
void *tup;
Assert(forward || (readptr->eflags & EXEC_FLAG_BACKWARD));
switch (state->status)
{
case TSS_INMEM:
*should_free = false;
if (forward)
{
if (readptr->eof_reached)
return NULL;
if (readptr->current < state->memtupcount)
{
/* We have another tuple, so return it */
return state->memtuples[readptr->current++];
}
readptr->eof_reached = true;
return NULL;
}
else
{
/*
* if all tuples are fetched already then we return last
* tuple, else tuple before last returned.
*/
if (readptr->eof_reached)
{
readptr->current = state->memtupcount;
readptr->eof_reached = false;
}
else
{
if (readptr->current <= state->memtupdeleted)
{
Assert(!state->truncated);
return NULL;
}
readptr->current--; /* last returned tuple */
}
if (readptr->current <= state->memtupdeleted)
{
Assert(!state->truncated);
return NULL;
}
return state->memtuples[readptr->current - 1];
}
break;
case TSS_WRITEFILE:
/* Skip state change if we'll just return NULL */
if (readptr->eof_reached && forward)
return NULL;
/*
* Switch from writing to reading.
*/
BufFileTell(state->myfile,
&state->writepos_file, &state->writepos_offset);
if (!readptr->eof_reached)
if (BufFileSeek(state->myfile,
readptr->file, readptr->offset,
SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
state->status = TSS_READFILE;
/* FALLTHROUGH */
case TSS_READFILE:
*should_free = true;
if (forward)
{
if ((tuplen = getlen(state, true)) != 0)
{
tup = READTUP(state, tuplen);
return tup;
}
else
{
readptr->eof_reached = true;
return NULL;
}
}
/*
* Backward.
*
* if all tuples are fetched already then we return last tuple,
* else tuple before last returned.
*
* Back up to fetch previously-returned tuple's ending length
* word. If seek fails, assume we are at start of file.
*/
if (BufFileSeek(state->myfile, 0, -(long) sizeof(unsigned int),
SEEK_CUR) != 0)
{
/* even a failed backwards fetch gets you out of eof state */
readptr->eof_reached = false;
Assert(!state->truncated);
return NULL;
}
tuplen = getlen(state, false);
if (readptr->eof_reached)
{
readptr->eof_reached = false;
/* We will return the tuple returned before returning NULL */
}
else
{
/*
* Back up to get ending length word of tuple before it.
*/
if (BufFileSeek(state->myfile, 0,
-(long) (tuplen + 2 * sizeof(unsigned int)),
SEEK_CUR) != 0)
{
/*
* If that fails, presumably the prev tuple is the first
* in the file. Back up so that it becomes next to read
* in forward direction (not obviously right, but that is
* what in-memory case does).
*/
if (BufFileSeek(state->myfile, 0,
-(long) (tuplen + sizeof(unsigned int)),
SEEK_CUR) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
Assert(!state->truncated);
return NULL;
}
tuplen = getlen(state, false);
}
/*
* Now we have the length of the prior tuple, back up and read it.
* Note: READTUP expects we are positioned after the initial
* length word of the tuple, so back up to that point.
*/
if (BufFileSeek(state->myfile, 0,
-(long) tuplen,
SEEK_CUR) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
tup = READTUP(state, tuplen);
return tup;
default:
elog(ERROR, "invalid tuplestore state");
return NULL; /* keep compiler quiet */
}
}
/*
* tuplestore_gettupleslot - exported function to fetch a MinimalTuple
*
* If successful, put tuple in slot and return true; else, clear the slot
* and return false.
*
* If copy is true, the slot receives a copied tuple (allocated in current
* memory context) that will stay valid regardless of future manipulations of
* the tuplestore's state. If copy is false, the slot may just receive a
* pointer to a tuple held within the tuplestore. The latter is more
* efficient but the slot contents may be corrupted if additional writes to
* the tuplestore occur. (If using tuplestore_trim, see comments therein.)
*/
bool
tuplestore_gettupleslot(Tuplestorestate *state, bool forward,
bool copy, TupleTableSlot *slot)
{
MinimalTuple tuple;
bool should_free;
tuple = (MinimalTuple) tuplestore_gettuple(state, forward, &should_free);
if (tuple)
{
if (copy && !should_free)
{
tuple = heap_copy_minimal_tuple(tuple);
should_free = true;
}
ExecStoreMinimalTuple(tuple, slot, should_free);
return true;
}
else
{
ExecClearTuple(slot);
return false;
}
}
/*
* tuplestore_advance - exported function to adjust position without fetching
*
* We could optimize this case to avoid palloc/pfree overhead, but for the
* moment it doesn't seem worthwhile.
*/
bool
tuplestore_advance(Tuplestorestate *state, bool forward)
{
void *tuple;
bool should_free;
tuple = tuplestore_gettuple(state, forward, &should_free);
if (tuple)
{
if (should_free)
pfree(tuple);
return true;
}
else
{
return false;
}
}
/*
* Advance over N tuples in either forward or back direction,
* without returning any data. N<=0 is a no-op.
* Returns true if successful, false if ran out of tuples.
*/
bool
tuplestore_skiptuples(Tuplestorestate *state, int64 ntuples, bool forward)
{
TSReadPointer *readptr = &state->readptrs[state->activeptr];
Assert(forward || (readptr->eflags & EXEC_FLAG_BACKWARD));
if (ntuples <= 0)
return true;
switch (state->status)
{
case TSS_INMEM:
if (forward)
{
if (readptr->eof_reached)
return false;
if (state->memtupcount - readptr->current >= ntuples)
{
readptr->current += ntuples;
return true;
}
readptr->current = state->memtupcount;
readptr->eof_reached = true;
return false;
}
else
{
if (readptr->eof_reached)
{
readptr->current = state->memtupcount;
readptr->eof_reached = false;
ntuples--;
}
if (readptr->current - state->memtupdeleted > ntuples)
{
readptr->current -= ntuples;
return true;
}
Assert(!state->truncated);
readptr->current = state->memtupdeleted;
return false;
}
break;
default:
/* We don't currently try hard to optimize other cases */
while (ntuples-- > 0)
{
void *tuple;
bool should_free;
tuple = tuplestore_gettuple(state, forward, &should_free);
if (tuple == NULL)
return false;
if (should_free)
pfree(tuple);
CHECK_FOR_INTERRUPTS();
}
return true;
}
}
/*
* dumptuples - remove tuples from memory and write to tape
*
* As a side effect, we must convert each read pointer's position from
* "current" to file/offset format. But eof_reached pointers don't
* need to change state.
*/
static void
dumptuples(Tuplestorestate *state)
{
int i;
for (i = state->memtupdeleted;; i++)
{
TSReadPointer *readptr = state->readptrs;
int j;
for (j = 0; j < state->readptrcount; readptr++, j++)
{
if (i == readptr->current && !readptr->eof_reached)
BufFileTell(state->myfile,
&readptr->file, &readptr->offset);
}
if (i >= state->memtupcount)
break;
WRITETUP(state, state->memtuples[i]);
}
state->memtupdeleted = 0;
state->memtupcount = 0;
}
/*
* tuplestore_rescan - rewind the active read pointer to start
*/
void
tuplestore_rescan(Tuplestorestate *state)
{
TSReadPointer *readptr = &state->readptrs[state->activeptr];
Assert(readptr->eflags & EXEC_FLAG_REWIND);
Assert(!state->truncated);
switch (state->status)
{
case TSS_INMEM:
readptr->eof_reached = false;
readptr->current = 0;
break;
case TSS_WRITEFILE:
readptr->eof_reached = false;
readptr->file = 0;
readptr->offset = 0L;
break;
case TSS_READFILE:
readptr->eof_reached = false;
if (BufFileSeek(state->myfile, 0, 0L, SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
break;
default:
elog(ERROR, "invalid tuplestore state");
break;
}
}
/*
* tuplestore_copy_read_pointer - copy a read pointer's state to another
*/
void
tuplestore_copy_read_pointer(Tuplestorestate *state,
int srcptr, int destptr)
{
TSReadPointer *sptr = &state->readptrs[srcptr];
TSReadPointer *dptr = &state->readptrs[destptr];
Assert(srcptr >= 0 && srcptr < state->readptrcount);
Assert(destptr >= 0 && destptr < state->readptrcount);
/* Assigning to self is a no-op */
if (srcptr == destptr)
return;
if (dptr->eflags != sptr->eflags)
{
/* Possible change of overall eflags, so copy and then recompute */
int eflags;
int i;
*dptr = *sptr;
eflags = state->readptrs[0].eflags;
for (i = 1; i < state->readptrcount; i++)
eflags |= state->readptrs[i].eflags;
state->eflags = eflags;
}
else
*dptr = *sptr;
switch (state->status)
{
case TSS_INMEM:
case TSS_WRITEFILE:
/* no work */
break;
case TSS_READFILE:
/*
* This case is a bit tricky since the active read pointer's
* position corresponds to the seek point, not what is in its
* variables. Assigning to the active requires a seek, and
* assigning from the active requires a tell, except when
* eof_reached.
*/
if (destptr == state->activeptr)
{
if (dptr->eof_reached)
{
if (BufFileSeek(state->myfile,
state->writepos_file,
state->writepos_offset,
SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
}
else
{
if (BufFileSeek(state->myfile,
dptr->file, dptr->offset,
SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in tuplestore temporary file: %m")));
}
}
else if (srcptr == state->activeptr)
{
if (!dptr->eof_reached)
BufFileTell(state->myfile,
&dptr->file,
&dptr->offset);
}
break;
default:
elog(ERROR, "invalid tuplestore state");
break;
}
}
/*
* tuplestore_trim - remove all no-longer-needed tuples
*
* Calling this function authorizes the tuplestore to delete all tuples
* before the oldest read pointer, if no read pointer is marked as requiring
* REWIND capability.
*
* Note: this is obviously safe if no pointer has BACKWARD capability either.
* If a pointer is marked as BACKWARD but not REWIND capable, it means that
* the pointer can be moved backward but not before the oldest other read
* pointer.
*/
void
tuplestore_trim(Tuplestorestate *state)
{
int oldest;
int nremove;
int i;
/*
* Truncation is disallowed if any read pointer requires rewind
* capability.
*/
if (state->eflags & EXEC_FLAG_REWIND)
return;
/*
* We don't bother trimming temp files since it usually would mean more
* work than just letting them sit in kernel buffers until they age out.
*/
if (state->status != TSS_INMEM)
return;
/* Find the oldest read pointer */
oldest = state->memtupcount;
for (i = 0; i < state->readptrcount; i++)
{
if (!state->readptrs[i].eof_reached)
oldest = Min(oldest, state->readptrs[i].current);
}
/*
* Note: you might think we could remove all the tuples before the oldest
* "current", since that one is the next to be returned. However, since
* tuplestore_gettuple returns a direct pointer to our internal copy of
* the tuple, it's likely that the caller has still got the tuple just
* before "current" referenced in a slot. So we keep one extra tuple
* before the oldest "current". (Strictly speaking, we could require such
* callers to use the "copy" flag to tuplestore_gettupleslot, but for
* efficiency we allow this one case to not use "copy".)
*/
nremove = oldest - 1;
if (nremove <= 0)
return; /* nothing to do */
Assert(nremove >= state->memtupdeleted);
Assert(nremove <= state->memtupcount);
/* Release no-longer-needed tuples */
for (i = state->memtupdeleted; i < nremove; i++)
{
FREEMEM(state, GetMemoryChunkSpace(state->memtuples[i]));
pfree(state->memtuples[i]);
state->memtuples[i] = NULL;
}
state->memtupdeleted = nremove;
/* mark tuplestore as truncated (used for Assert crosschecks only) */
state->truncated = true;
/*
* If nremove is less than 1/8th memtupcount, just stop here, leaving the
* "deleted" slots as NULL. This prevents us from expending O(N^2) time
* repeatedly memmove-ing a large pointer array. The worst case space
* wastage is pretty small, since it's just pointers and not whole tuples.
*/
if (nremove < state->memtupcount / 8)
return;
/*
* Slide the array down and readjust pointers.
*
* In mergejoin's current usage, it's demonstrable that there will always
* be exactly one non-removed tuple; so optimize that case.
*/
if (nremove + 1 == state->memtupcount)
state->memtuples[0] = state->memtuples[nremove];
else
memmove(state->memtuples, state->memtuples + nremove,
(state->memtupcount - nremove) * sizeof(void *));
state->memtupdeleted = 0;
state->memtupcount -= nremove;
for (i = 0; i < state->readptrcount; i++)
{
if (!state->readptrs[i].eof_reached)
state->readptrs[i].current -= nremove;
}
}
/*
* tuplestore_in_memory
*
* Returns true if the tuplestore has not spilled to disk.
*
* XXX exposing this is a violation of modularity ... should get rid of it.
*/
bool
tuplestore_in_memory(Tuplestorestate *state)
{
return (state->status == TSS_INMEM);
}
/*
* Tape interface routines
*/
static unsigned int
getlen(Tuplestorestate *state, bool eofOK)
{
unsigned int len;
size_t nbytes;
nbytes = BufFileRead(state->myfile, (void *) &len, sizeof(len));
if (nbytes == sizeof(len))
return len;
if (nbytes != 0 || !eofOK)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from tuplestore temporary file: %m")));
return 0;
}
/*
* Routines specialized for HeapTuple case
*
* The stored form is actually a MinimalTuple, but for largely historical
* reasons we allow COPYTUP to work from a HeapTuple.
*
* Since MinimalTuple already has length in its first word, we don't need
* to write that separately.
*/
static void *
copytup_heap(Tuplestorestate *state, void *tup)
{
MinimalTuple tuple;
tuple = minimal_tuple_from_heap_tuple((HeapTuple) tup);
USEMEM(state, GetMemoryChunkSpace(tuple));
return (void *) tuple;
}
static void
writetup_heap(Tuplestorestate *state, void *tup)
{
MinimalTuple tuple = (MinimalTuple) tup;
/* the part of the MinimalTuple we'll write: */
char *tupbody = (char *) tuple + MINIMAL_TUPLE_DATA_OFFSET;
unsigned int tupbodylen = tuple->t_len - MINIMAL_TUPLE_DATA_OFFSET;
/* total on-disk footprint: */
unsigned int tuplen = tupbodylen + sizeof(int);
if (BufFileWrite(state->myfile, (void *) &tuplen,
sizeof(tuplen)) != sizeof(tuplen))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to tuplestore temporary file: %m")));
if (BufFileWrite(state->myfile, (void *) tupbody,
tupbodylen) != (size_t) tupbodylen)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to tuplestore temporary file: %m")));
if (state->backward) /* need trailing length word? */
if (BufFileWrite(state->myfile, (void *) &tuplen,
sizeof(tuplen)) != sizeof(tuplen))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not write to tuplestore temporary file: %m")));
FREEMEM(state, GetMemoryChunkSpace(tuple));
heap_free_minimal_tuple(tuple);
}
static void *
readtup_heap(Tuplestorestate *state, unsigned int len)
{
unsigned int tupbodylen = len - sizeof(int);
unsigned int tuplen = tupbodylen + MINIMAL_TUPLE_DATA_OFFSET;
MinimalTuple tuple = (MinimalTuple) palloc(tuplen);
char *tupbody = (char *) tuple + MINIMAL_TUPLE_DATA_OFFSET;
USEMEM(state, GetMemoryChunkSpace(tuple));
/* read in the tuple proper */
tuple->t_len = tuplen;
if (BufFileRead(state->myfile, (void *) tupbody,
tupbodylen) != (size_t) tupbodylen)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from tuplestore temporary file: %m")));
if (state->backward) /* need trailing length word? */
if (BufFileRead(state->myfile, (void *) &tuplen,
sizeof(tuplen)) != sizeof(tuplen))
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from tuplestore temporary file: %m")));
return (void *) tuple;
}