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Fix representation of SORT_TYPE_STILL_IN_PROGRESS. 

It turns out that the code did indeed rely on a zeroed
TuplesortInstrumentation.sortMethod field to indicate
"this worker never did anything", although it seems the
issue only comes up during certain race-condition-y cases.

Hence, rearrange the TuplesortMethod enum to restore
SORT_TYPE_STILL_IN_PROGRESS to having the value zero,
and add some comments reinforcing that that isn't optional.

Also future-proof a loop over the possible values of the enum.
sizeof(bits32) happened to be the correct limit value,
but only by purest coincidence.

Per buildfarm and local investigation.

Discussion: https://postgr.es/m/12222.1586223974@sss.pgh.pa.us
This commit is contained in:
Tom Lane 2020-04-06 22:22:13 -04:00
parent 4c04be9b05
commit c7654f6a37
2 changed files with 19 additions and 13 deletions
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12
src/backend/commands/explain.c
View File

@ -2762,14 +2762,14 @@ show_incremental_sort_group_info(IncrementalSortGroupInfo *groupInfo,
List *methodNames = NIL;
/* Generate a list of sort methods used across all groups. */
for (int bit = 0; bit < sizeof(bits32); ++bit)
for (int bit = 0; bit < NUM_TUPLESORTMETHODS; bit++)
{
if (groupInfo->sortMethods & (1 << bit))
{
TuplesortMethod sortMethod = (1 << bit);
const char *methodName;
TuplesortMethod sortMethod = (1 << bit);
if (groupInfo->sortMethods & sortMethod)
{
const char *methodName = tuplesort_method_name(sortMethod);
methodName = tuplesort_method_name(sortMethod);
methodNames = lappend(methodNames, unconstify(char *, methodName));
}
}

20
src/include/utils/tuplesort.h
View File

@ -62,18 +62,24 @@ typedef struct SortCoordinateData *SortCoordinate;
* TuplesortInstrumentation can't contain any pointers because we
* sometimes put it in shared memory.
*
* TuplesortMethod is used in a bitmask in Increment Sort's shared memory
* instrumentation so needs to have each value be a separate bit.
* The parallel-sort infrastructure relies on having a zero TuplesortMethod
* indicate that a worker never did anything, so we assign zero to
* SORT_TYPE_STILL_IN_PROGRESS. The other values of this enum can be
* OR'ed together to represent a situation where different workers used
* different methods, so we need a separate bit for each one. Keep the
* NUM_TUPLESORTMETHODS constant in sync with the number of bits!
*/
typedef enum
{
SORT_TYPE_STILL_IN_PROGRESS = 1 << 0,
SORT_TYPE_TOP_N_HEAPSORT = 1 << 1,
SORT_TYPE_QUICKSORT = 1 << 2,
SORT_TYPE_EXTERNAL_SORT = 1 << 3,
SORT_TYPE_EXTERNAL_MERGE = 1 << 4
SORT_TYPE_STILL_IN_PROGRESS = 0,
SORT_TYPE_TOP_N_HEAPSORT = 1 << 0,
SORT_TYPE_QUICKSORT = 1 << 1,
SORT_TYPE_EXTERNAL_SORT = 1 << 2,
SORT_TYPE_EXTERNAL_MERGE = 1 << 3
} TuplesortMethod;
#define NUM_TUPLESORTMETHODS 4
typedef enum
{
SORT_SPACE_TYPE_DISK,