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Fix ancient docs/comments thinko: XID comparison is mod 2^32, not 2^31.

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Pointed out by Gianni Ciolli.
This commit is contained in:
Tom Lane
2013-12-12 12:40:07 -05:00
parent 884c6384a2
commit 85eb066ecd
2 changed files with 2 additions and 2 deletions
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2
doc/src/sgml/maintenance.sgml
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@ -356,7 +356,7 @@
<productname>PostgreSQL</productname> distinguishes a special XID <productname>PostgreSQL</productname> distinguishes a special XID
<literal>FrozenXID</>. This XID is always considered older <literal>FrozenXID</>. This XID is always considered older
than every normal XID. Normal XIDs are than every normal XID. Normal XIDs are
compared using modulo-2<superscript>31</> arithmetic. This means compared using modulo-2<superscript>32</> arithmetic. This means
that for every normal XID, there are two billion XIDs that are that for every normal XID, there are two billion XIDs that are
<quote>older</> and two billion that are <quote>newer</>; another <quote>older</> and two billion that are <quote>newer</>; another
way to say it is that the normal XID space is circular with no way to say it is that the normal XID space is circular with no

2
src/backend/access/transam/transam.c
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@ -305,7 +305,7 @@ TransactionIdPrecedes(TransactionId id1, TransactionId id2)
{ {
/* /*
* If either ID is a permanent XID then we can just do unsigned * If either ID is a permanent XID then we can just do unsigned
* comparison. If both are normal, do a modulo-2^31 comparison. * comparison. If both are normal, do a modulo-2^32 comparison.
*/ */
int32 diff; int32 diff;