diff options
Diffstat (limited to 'src/include/storage/procnumber.h')
| -rw-r--r-- | src/include/storage/procnumber.h | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/src/include/storage/procnumber.h b/src/include/storage/procnumber.h index 7cf981ab673..75c2c7a17c0 100644 --- a/src/include/storage/procnumber.h +++ b/src/include/storage/procnumber.h @@ -26,6 +26,19 @@ typedef int ProcNumber; #define INVALID_PROC_NUMBER (-1) /* + * Note: MAX_BACKENDS_BITS is 18 as that is the space available for buffer + * refcounts in buf_internals.h. This limitation could be lifted by using a + * 64bit state; but it's unlikely to be worthwhile as 2^18-1 backends exceed + * currently realistic configurations. Even if that limitation were removed, + * we still could not a) exceed 2^23-1 because inval.c stores the ProcNumber + * as a 3-byte signed integer, b) INT_MAX/4 because some places compute + * 4*MaxBackends without any overflow check. This is rechecked in the + * relevant GUC check hooks and in RegisterBackgroundWorker(). + */ +#define MAX_BACKENDS_BITS 18 +#define MAX_BACKENDS ((1U << MAX_BACKENDS_BITS)-1) + +/* * Proc number of this backend (same as GetNumberFromPGProc(MyProc)) */ extern PGDLLIMPORT ProcNumber MyProcNumber; |