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Fix off-by-one error in txid_status().

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The transaction ID returned by GetNextXidAndEpoch() is in the future,
so we can't attempt to access its status or we might try to read a
CLOG page that doesn't exist.  The > vs >= confusion probably stemmed
from the choice of a variable name containing the word "last" instead
of "next", so fix that too.

Back-patch to 10 where the function arrived.

Author: Thomas Munro
Discussion: https://postgr.es/m/CA%2BhUKG%2Buua_BV5cyfsioKVN2d61Lukg28ECsWTXKvh%3DBtN2DPA%40mail.gmail.com
This commit is contained in:
Thomas Munro 2019-03-27 21:16:50 +13:00
parent 5601f9fb97
commit 339927797c
1 changed files with 4 additions and 4 deletions
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8
src/backend/utils/adt/txid.c
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@ -113,9 +113,9 @@ TransactionIdInRecentPast(uint64 xid_with_epoch, TransactionId *extracted_xid)
uint32 xid_epoch = (uint32) (xid_with_epoch >> 32);
TransactionId xid = (TransactionId) xid_with_epoch;
uint32 now_epoch;
TransactionId now_epoch_last_xid;
TransactionId now_epoch_next_xid;
GetNextXidAndEpoch(&now_epoch_last_xid, &now_epoch);
GetNextXidAndEpoch(&now_epoch_next_xid, &now_epoch);
if (extracted_xid != NULL)
*extracted_xid = xid;
@ -129,7 +129,7 @@ TransactionIdInRecentPast(uint64 xid_with_epoch, TransactionId *extracted_xid)
/* If the transaction ID is in the future, throw an error. */
if (xid_epoch > now_epoch
|| (xid_epoch == now_epoch && xid > now_epoch_last_xid))
|| (xid_epoch == now_epoch && xid >= now_epoch_next_xid))
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("transaction ID %s is in the future",
@ -151,7 +151,7 @@ TransactionIdInRecentPast(uint64 xid_with_epoch, TransactionId *extracted_xid)
* CLOG entry is guaranteed to still exist.
*/
if (xid_epoch + 1 < now_epoch
|| (xid_epoch + 1 == now_epoch && xid < now_epoch_last_xid)
|| (xid_epoch + 1 == now_epoch && xid < now_epoch_next_xid)
|| TransactionIdPrecedes(xid, ShmemVariableCache->oldestClogXid))
return false;