Hackers,
While working on the problem of XID wraparound within the LISTEN/NOTIFY
system, I tried to increment XIDs by more than one per transaction.
This leads to a number of test failures, many which look like:
+ERROR: could not access status of transaction 7485
+DETAIL: Could not read from file "pg_subtrans/" at offset 24576:
read too few bytes.
I might not have read the right documentation, but
I do not see anything in src/backend/access/transam/README nor elsewhere
documenting a design decision or assumption that transaction IDs must
be assigned contiguously. I suppose this is such a fundamental
assumption that it is completely implicit and nobody thought to document
it, but I'd like to check for two reasons:
First, I'd like a good method of burning through transaction ids in
tests designed to check for problems in XID wrap-around.
Second, I'd like to add Asserts where appropriate regarding this
assumption. It seems strange to me that I should have gotten as far
as a failing read() without having tripped an Assert somewhere along the
way.
To duplicate the errors I hit, you can either apply this simple change:
diff --git a/src/include/access/transam.h b/src/include/access/transam.h
index 33fd052156..360b7335bb 100644
--- a/src/include/access/transam.h
+++ b/src/include/access/transam.h
@@ -83,7 +83,7 @@ FullTransactionIdFromEpochAndXid(uint32 epoch,
TransactionId xid)
static inline void
FullTransactionIdAdvance(FullTransactionId *dest)
{
- dest->value++;
+ dest->value += 2;
while (XidFromFullTransactionId(*dest) < FirstNormalTransactionId)
dest->value++;
}
or apply the much larger WIP patch, attached, and then be sure to
provide the --enable-xidcheck flag to configure before building.
--
Mark Dilger
diff --git a/configure b/configure
index 1d88983b34..909907127a 100755
--- a/configure
+++ b/configure
@@ -841,6 +841,7 @@ with_CC
with_llvm
enable_depend
enable_cassert
+enable_xidcheck
enable_thread_safety
with_icu
with_tcl
@@ -1521,6 +1522,7 @@ Optional Features:
--enable-tap-tests enable TAP tests (requires Perl and IPC::Run)
--enable-depend turn on automatic dependency tracking
--enable-cassertenable assertion checks (for debugging)
+ --enable-xidcheck enable transactionid checks (for debugging)
--disable-thread-safety disable thread-safety in client libraries
--disable-largefile omit support for large files
@@ -7197,6 +7199,36 @@ fi
+#
+# Enable transactionid checks
+#
+
+
+# Check whether --enable-xidcheck was given.
+if test "${enable_xidcheck+set}" = set; then :
+ enableval=$enable_xidcheck;
+ case $enableval in
+yes)
+
+$as_echo "#define USE_XID_CHECKING 1" >>confdefs.h
+
+ ;;
+no)
+ :
+ ;;
+*)
+ as_fn_error $? "no argument expected for --enable-xidcheck option"
"$LINENO" 5
+ ;;
+ esac
+
+else
+ enable_xidcheck=no
+
+fi
+
+
+
+
#
# Include directories
#
diff --git a/configure.in b/configure.in
index a2cb20b5e3..5aac6c24f1 100644
--- a/configure.in
+++ b/configure.in
@@ -680,6 +680,14 @@ PGAC_ARG_BOOL(enable, cassert, no, [enable assertion
checks (for debugging)],
[Define to 1 to build with assertion checks.
(--enable-cassert)])])
+#
+# Enable transactionid checks
+#
+PGAC_ARG_BOOL(enable, xidcheck, no, [enable transactionid checks (for
debugging)],
+ [AC_DEFINE([USE_XID_CHECKING], 1,
+ [Define to 1 to build with transactionid checks.
(--enable-xidcheck)])])
+
+
#
# Include directories
#
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d4d1fe45cc..a3dbe27640 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -9246,6 +9246,26 @@ dynamic_library_path =
'C:\tools\postgresql;H:\my_project\lib;$libdir'
+
+ debug_xidcheck (boolean)
+
+ debug_xidcheck configuration
parameter
+
+
+
+
+Reports whether PostgreSQL has been built
+with transaction id checking enabled. That is the case if the
+macro USE_XID_CHECKING is defined
+when PostgreSQL is built (accomplished
+e.g. by the configure option
+--enable-xidcheck). By
+default PostgreSQL is built without
+transaction id checking.
+
+
+
+
integer_datetimes (boolean)
diff --git a/doc/src/sgml/installation.sgml b/doc/src/sgml/installation.sgml
index 9c10a897f1..eedfd021a0 100644
--- a/doc/src/sgml/installation.sgml
+++ b/doc/src/sgml/installation.sgml
@@ -1524,6 +1524,19 @@ build-postgresql:
+
+ --enable-xidcheck
+
+
+ Enables transaction ID checks in the server,
which test
+ the 64-bit transaction ID management. This may prove valuable for
+ code development purposes, but enabling this feature will consume a
small
+ amount of sh
