database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-11-09 06:21:09 +03:00
Code Activity

Remove all use of ThisTimeLineID global variable outside of xlog.c

Browse Source 
All such code deals with this global variable in one of three ways.
Sometimes the same functions use it in more than one of these ways
at the same time.

First, sometimes it's an implicit argument to one or more functions
being called in xlog.c or elsewhere, and must be set to the
appropriate value before calling those functions lest they
misbehave. In those cases, it is now passed as an explicit argument
instead.

Second, sometimes it's used to obtain the current timeline after
the end of recovery, i.e. the timeline to which WAL is being
written and flushed. Such code now calls GetWALInsertionTimeLine()
or relies on the new out parameter added to GetFlushRecPtr().

Third, sometimes it's used during recovery to store the current
replay timeline. That can change, so such code must generally
update the value before each use. It can still do that, but must
now use a local variable instead.

The net effect of these changes is to reduce by a fair amount the
amount of code that is directly accessing this global variable.
That's good, because history has shown that we don't always think
clearly about which timeline ID it's supposed to contain at any
given point in time, or indeed, whether it has been or needs to
be initialized at any given point in the code.

Patch by me, reviewed and tested by Michael Paquier, Amul Sul, and
Álvaro Herrera.

Discussion: https://postgr.es/m/CA+TgmobfAAqhfWa1kaFBBFvX+5CjM=7TE=n4r4Q1o2bjbGYBpA@mail.gmail.com
This commit is contained in:
Robert Haas
2021-11-05 12:50:01 -04:00
parent caf1f675b8
commit e997a0c642
13 changed files with 169 additions and 132 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
src/backend/access/transam/twophase.c
View File

@@ -1373,11 +1373,7 @@ ReadTwoPhaseFile(TransactionId xid, bool missing_ok)
* twophase files and ReadTwoPhaseFile should be used instead.
*
* Note clearly that this function can access WAL during normal operation,
* similarly to the way WALSender or Logical Decoding would do. While
* accessing WAL, read_local_xlog_page() may change ThisTimeLineID,
* particularly if this routine is called for the end-of-recovery checkpoint
* in the checkpointer itself, so save the current timeline number value
* and restore it once done.
* similarly to the way WALSender or Logical Decoding would do.
*/
static void
XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
@@ -1385,7 +1381,6 @@ XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
XLogRecord *record;
XLogReaderState *xlogreader;
char *errormsg;
TimeLineID save_currtli = ThisTimeLineID;
xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
XL_ROUTINE(.page_read = &read_local_xlog_page,
@@ -1401,13 +1396,6 @@ XlogReadTwoPhaseData(XLogRecPtr lsn, char **buf, int *len)
XLogBeginRead(xlogreader, lsn);
record = XLogReadRecord(xlogreader, &errormsg);
/*
* Restore immediately the timeline where it was previously, as
* read_local_xlog_page() could have changed it if the record was read
* while recovery was finishing or if the timeline has jumped in-between.
*/
ThisTimeLineID = save_currtli;
if (record == NULL)
ereport(ERROR,
(errcode_for_file_access(),