[HACKERS] Fix GetOldestXmin comment - Mailing list pgsql-hackers

Hi,

While reading source code, I realized that comment of GetOldestXmin mentions;

  * if rel = NULL and there are no transactions running in the current
  * database, GetOldestXmin() returns latestCompletedXid.

However, in that case if I understand correctly GetOldestXmin()
actually returns latestCompletedXid + 1 as follows;

  /*
   * We initialize the MIN() calculation with latestCompletedXid + 1. This
   * is a lower bound for the XIDs that might appear in the ProcArray later,
   * and so protects us against overestimating the result due to future
   * additions.
   */
  result = ShmemVariableCache->latestCompletedXid;
  Assert(TransactionIdIsNormal(result));
  TransactionIdAdvance(result);

Attached patch fixes the top comment of GetOldestXmin.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center

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