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logtape.c: allocate read buffer even for an empty tape.

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Prior to this commit, the read buffer was allocated at the time the tape
was rewound; but as an optimization, would not be allocated at all if
the tape was empty.

That optimization meant that it was valid to have a rewound tape with
the buffer set to NULL, but only if a number of conditions were met
and only if the API was used properly. After 7fdd919a refactored the
code to support lazily-allocating the buffer, Coverity started
complaining.

The optimization for empty tapes doesn't seem important, so just
allocate the buffer whether the tape has any data or not.

Discussion: https://postgr.es/m/20351.1581868306%40sss.pgh.pa.us
This commit is contained in:
Jeff Davis 2020-02-18 12:31:24 -08:00
parent 0074919794
commit 8021985d79
1 changed files with 5 additions and 11 deletions
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16
src/backend/utils/sort/logtape.c
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@ -544,11 +544,8 @@ ltsConcatWorkerTapes(LogicalTapeSet *lts, TapeShare *shared,
static void
ltsInitReadBuffer(LogicalTapeSet *lts, LogicalTape *lt)
{
if (lt->firstBlockNumber != -1L)
{
Assert(lt->buffer_size > 0);
lt->buffer = palloc(lt->buffer_size);
}
Assert(lt->buffer_size > 0);
lt->buffer = palloc(lt->buffer_size);
/* Read the first block, or reset if tape is empty */
lt->nextBlockNumber = lt->firstBlockNumber;
@ -839,13 +836,10 @@ LogicalTapeRewindForRead(LogicalTapeSet *lts, int tapenum, size_t buffer_size)
/* Allocate a read buffer (unless the tape is empty) */
if (lt->buffer)
pfree(lt->buffer);
/* the buffer is lazily allocated, but set the size here */
lt->buffer = NULL;
lt->buffer_size = 0;
if (lt->firstBlockNumber != -1L)
{
/* the buffer is lazily allocated, but set the size here */
lt->buffer_size = buffer_size;
}
lt->buffer_size = buffer_size;
}
/*