From 48188e1621bb6711e7d092bee48523b18cd80177 Mon Sep 17 00:00:00 2001
From: Tom Lane
Date: Sun, 5 Nov 2006 22:42:10 +0000
Subject: Fix recently-understood problems with handling of XID freezing,
particularly in PITR scenarios. We now WAL-log the replacement of old XIDs
with FrozenTransactionId, so that such replacement is guaranteed to propagate
to PITR slave databases. Also, rather than relying on hint-bit updates to be
preserved, pg_clog is not truncated until all instances of an XID are known
to have been replaced by FrozenTransactionId. Add new GUC variables and
pg_autovacuum columns to allow management of the freezing policy, so that
users can trade off the size of pg_clog against the amount of freezing work
done. Revise the already-existing code that forces autovacuum of tables
approaching the wraparound point to make it more bulletproof; also, revise
the autovacuum logic so that anti-wraparound vacuuming is done per-table
rather than per-database. initdb forced because of changes in pg_class,
pg_database, and pg_autovacuum catalogs. Heikki Linnakangas, Simon Riggs,
and Tom Lane.
---
doc/src/sgml/catalogs.sgml | 83 ++++++++++++++++++++++++----------------------
1 file changed, 43 insertions(+), 40 deletions(-)
(limited to 'doc/src/sgml/catalogs.sgml')
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index af28a26b1a0..1ade58644e9 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -1,4 +1,4 @@
-
+
@@ -1241,6 +1241,20 @@
Custom vacuum_cost_limit parameter
+
+
+ freeze_min_age
+ integer
+
+ Custom vacuum_freeze_min_age parameter
+
+
+
+ freeze_max_age
+ integer
+
+ Custom autovacuum_freeze_max_age parameter
+
@@ -1258,6 +1272,17 @@
live tuples currently estimated to be in the relation.
+
+ Also, the autovacuum daemon will perform a VACUUM operation
+ to prevent transaction ID wraparound if the table's
+ pg_class.relfrozenxid field attains an age
+ of more than freeze_max_age transactions, whether the table
+ has been changed or not. The system will launch autovacuum to perform
+ such VACUUMs even if autovacuum is otherwise disabled.
+ See for more about wraparound
+ prevention.
+
+
Any of the numerical fields can contain -1 (or indeed
any negative value) to indicate that the system-wide default should
@@ -1266,6 +1291,10 @@
autovacuum_vacuum_cost_delay configuration parameter,
or from vacuum_cost_delay if the former is set to a negative
value. The same applies to vac_cost_limit.
+ Also, autovacuum will ignore attempts to set a per-table
+ freeze_max_age larger than the system-wide setting (it can only be set
+ smaller), and the freeze_min_age value will be limited to half the
+ system-wide autovacuum_freeze_max_age setting.
@@ -1633,26 +1662,15 @@
- relminxid
+ relfrozenxid
xid
- The minimum transaction ID present in all rows in this table. This
- value is used to determine the database-global
- pg_database.datminxid value.
-
-
-
-
- relvacuumxid
- xid
-
-
- The transaction ID that was used as cleaning point as of the last vacuum
- operation. All rows inserted, updated or deleted in this table by
- transactions whose IDs are below this one have been marked as known good
- or deleted. This is used to determine the database-global
- pg_database.datvacuumxid value.
+ All transaction IDs before this one have been replaced with a permanent
+ (frozen) transaction ID in this table. This is used to track
+ whether the table needs to be vacuumed in order to prevent transaction
+ ID wraparound or to allow pg_clog to be shrunk. Zero
+ (InvalidTransactionId) if the relation is not a table.
@@ -2035,31 +2053,16 @@
- datvacuumxid
- xid
-
-
- The transaction ID that was used as cleaning point as of the last vacuum
- operation. All rows inserted or deleted by transaction IDs before this one
- have been marked as known good or deleted. This
- is used to determine when commit-log space can be recycled.
- If InvalidTransactionId, then the minimum is unknown and can be
- determined by scanning pg_class.relvacuumxid.
-
-
-
-
- datminxid
+ datfrozenxid
xid
- The minimum transaction ID present in all tables in this database.
- All rows inserted by transaction IDs before this one have been
- relabeled with a permanent (frozen) transaction ID in this
- database. This is useful to check whether a database must be
- vacuumed soon to avoid transaction ID wrap-around problems.
- If InvalidTransactionId, then the minimum is unknown and can be
- determined by scanning pg_class.relminxid.
+ All transaction IDs before this one have been replaced with a permanent
+ (frozen) transaction ID in this database. This is used to
+ track whether the database needs to be vacuumed in order to prevent
+ transaction ID wraparound or to allow pg_clog to be shrunk.
+ It is the minimum of the per-table
+ pg_class.relfrozenxid values.
--
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