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Diffstat (limited to 'src/backend/access/transam/xlog.c')
| -rw-r--r-- | src/backend/access/transam/xlog.c | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 88ad51f9e7d..a636bb6d2b0 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -4889,15 +4889,16 @@ BootStrapXLOG(void) * field, as being about as unique as we can easily get. (Think not to * use random(), since it hasn't been seeded and there's no portable way * to seed it other than the system clock value...) The upper half of the - * uint64 value is just the tv_sec part, while the lower half is the XOR - * of tv_sec and tv_usec. This is to ensure that we don't lose uniqueness - * unnecessarily if "uint64" is really only 32 bits wide. A person - * knowing this encoding can determine the initialization time of the - * installation, which could perhaps be useful sometimes. + * uint64 value is just the tv_sec part, while the lower half contains the + * tv_usec part (which must fit in 20 bits), plus 12 bits from our current + * PID for a little extra uniqueness. A person knowing this encoding can + * determine the initialization time of the installation, which could + * perhaps be useful sometimes. */ gettimeofday(&tv, NULL); sysidentifier = ((uint64) tv.tv_sec) << 32; - sysidentifier |= (uint32) (tv.tv_sec | tv.tv_usec); + sysidentifier |= ((uint64) tv.tv_usec) << 12; + sysidentifier |= getpid() & 0xFFF; /* First timeline ID is always 1 */ ThisTimeLineID = 1; |