/*
* 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;
/* FALL THRU into READFILE case */
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 */
}
}
/*
* 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, TuplestorePos *pos, bool forward,
bool *should_free)
{
uint32 tuplen;
void *tup;
Assert(forward || (state->eflags & EXEC_FLAG_BACKWARD));
switch (state->status)
{
case TSS_INMEM:
*should_free = false;
if (forward)
{
if (pos->current < state->memtupcount)
return state->memtuples[pos->current++];
pos->eof_reached = true;
return NULL;
}
else
{
if (pos->current <= 0)
return NULL;
/*
* if all tuples are fetched already then we return last
* tuple, else - tuple before last returned.
*/
if (pos->eof_reached)
pos->eof_reached = false;
else
{
pos->current--; /* last returned tuple */
if (pos->current <= 0)
return NULL;
}
return state->memtuples[pos->current - 1];
}
break;
case TSS_WRITEFILE:
/* Skip state change if we'll just return NULL */
if (pos->eof_reached && forward)
return NULL;
/*
* Switch from writing to reading.
*/
BufFileTell(state->myfile,
&pos->writepos_offset);
if (!pos->eof_reached)
if (BufFileSeek(state->myfile,
pos->readpos_offset,
SEEK_SET) != 0)
elog(ERROR, "seek failed");
state->status = TSS_READFILE;
/* FALL THRU into READFILE case */
case TSS_READFILE:
*should_free = true;
if (forward)
{
if ((tuplen = getlen(state, pos, true)) != 0)
{
tup = READTUP(state, pos, tuplen);
/* CDB XXX XXX XXX XXX */
/* MPP-1347: EXPLAIN ANALYZE shows runaway memory usage.
* Readtup does a usemem, but the free happens in
* ExecStoreTuple. Do a free so state->availMem
* doesn't go massively negative to screw up
* stats. It would be better to interrogate the
* heap for actual memory usage than use this
* homemade accounting.
*/
FREEMEM(state, GetMemoryChunkSpace(tup));
/* CDB XXX XXX XXX XXX */
return tup;
}
else
{
pos->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.
*/
insist_log(false, "Backward scanning of tuplestores are not supported at this time");
if (BufFileSeek(state->myfile, -(long) sizeof(uint32) /* offset */,
SEEK_CUR) != 0)
return NULL;
tuplen = getlen(state, pos, false);
if (pos->eof_reached)
{
pos->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,
-(long) (tuplen + 2 * sizeof(uint32)) /* offset */,
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,
-(long) (tuplen + sizeof(uint32)) /* offset */,
SEEK_CUR) != 0)
elog(ERROR, "bogus tuple length in backward scan");
return NULL;
}
tuplen = getlen(state, pos, 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,
-(long) tuplen /* offset */,
SEEK_CUR) != 0)
elog(ERROR, "bogus tuple length in backward scan");
tup = READTUP(state, pos, tuplen);
return tup;
default:
elog(ERROR, "invalid tuplestore state");
return NULL; /* keep compiler quiet */
}
}
