database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-21 16:02:15 +03:00
Code Activity

Back-patch contrib/vacuumlo's new -l (limit) option into 9.0 and 9.1.

Browse Source 
Since 9.0, removing lots of large objects in a single transaction risks
exceeding max_locks_per_transaction, because we merged large object removal
into the generic object-drop mechanism, which takes out an exclusive lock
on each object to be dropped.  This creates a hazard for contrib/vacuumlo,
which has historically tried to drop all unreferenced large objects in one
transaction.  There doesn't seem to be any correctness requirement to do it
that way, though; we only need to drop enough large objects per transaction
to amortize the commit costs.

To prevent a regression from pre-9.0 releases wherein vacuumlo worked just
fine, back-patch commits b69f2e3640 and
64c604898e, which break vacuumlo's deletions
into multiple transactions with a user-controllable upper limit on the
number of objects dropped per transaction.

Tim Lewis, Robert Haas, Tom Lane
This commit is contained in:
Tom Lane
2012-03-21 13:04:12 -04:00
parent d4a68363af
commit 3bf25a2a16
2 changed files with 135 additions and 34 deletions
Download Patch File Download Diff File Expand all files Collapse all files

24
doc/src/sgml/vacuumlo.sgml
View File

@ -49,6 +49,19 @@ vacuumlo [options] database [database2 ... databaseN]
</listitem>
</varlistentry>
<varlistentry>
<term><option>-l</option> <replaceable>limit</></term>
<listitem>
<para>
Remove no more than <replaceable>limit</> large objects per
transaction (default 1000). Since the server acquires a lock per LO
removed, removing too many LOs in one transaction risks exceeding
<xref linkend="guc-max-locks-per-transaction">. Set the limit to
zero if you want all removals done in a single transaction.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>-U</option> <replaceable>username</></term>
<listitem>
@ -75,7 +88,7 @@ vacuumlo [options] database [database2 ... databaseN]
<listitem>
<para>
Force <application>vacuumlo</application> to prompt for a
password before connecting to a database.
password before connecting to a database.
</para>
<para>
@ -110,18 +123,19 @@ vacuumlo [options] database [database2 ... databaseN]
<title>Method</title>
<para>
First, it builds a temporary table which contains all of the OIDs of the
large objects in that database.
First, <application>vacuumlo</> builds a temporary table which contains all
of the OIDs of the large objects in the selected database.
</para>
<para>
It then scans through all columns in the database that are of type
<type>oid</> or <type>lo</>, and removes matching entries from the
temporary table.
temporary table. (Note: only types with these names are considered;
in particular, domains over them are not considered.)
</para>
<para>
The remaining entries in the temp table identify orphaned LOs.
The remaining entries in the temporary table identify orphaned LOs.
These are removed.
</para>
</sect2>