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Tweak mvcc time format so rollovers are not an issue

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Former-commit-id: 14d01ec7bd6f20aea1ed51a1056d02d99583c6d2
This commit is contained in:
John Sully 2019-04-20 01:03:08 -04:00
parent d6be236697
commit fd65ef689a
2 changed files with 6 additions and 2 deletions
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4
src/server.cpp
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@ -4887,14 +4887,14 @@ uint64_t getMvccTstamp()
void incrementMvccTstamp() void incrementMvccTstamp()
{ {
uint64_t msPrev = server.mvcc_tstamp >> 22; uint64_t msPrev = server.mvcc_tstamp >> 20;
if (msPrev >= (uint64_t)server.mstime) // we can be greater if the count overflows if (msPrev >= (uint64_t)server.mstime) // we can be greater if the count overflows
{ {
atomicIncr(server.mvcc_tstamp, 1); atomicIncr(server.mvcc_tstamp, 1);
} }
else else
{ {
server.mvcc_tstamp = ((uint64_t)server.mstime) << 22; server.mvcc_tstamp = ((uint64_t)server.mstime) << 20;
} }
} }

4
src/server.h
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@ -1524,6 +1524,10 @@ struct redisServer {
unsigned char uuid[UUID_BINARY_LEN]; /* This server's UUID - populated on boot */ unsigned char uuid[UUID_BINARY_LEN]; /* This server's UUID - populated on boot */
struct fastlock flock; struct fastlock flock;
// Format:
// Lower 20 bits: a counter incrementing for each command executed in the same millisecond
// Upper 44 bits: mstime (least significant 44-bits) enough for ~500 years before rollover from date of addition
uint64_t mvcc_tstamp; uint64_t mvcc_tstamp;
}; };