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0d1fe9f74e
Previously we initialized pages when bulk extending in
RelationAddExtraBlocks(). That has a major disadvantage: It ties
RelationAddExtraBlocks() to heap, as other types of storage are likely
to need different amounts of special space, have different amount of
free space (previously determined by PageGetHeapFreeSpace()).
That we're relying on initializing pages, but not WAL logging the
initialization, also means the risk for getting
"WARNING: relation \"%s\" page %u is uninitialized --- fixing"
style warnings in vacuums after crashes/immediate shutdowns, is
considerably higher. The warning sounds much more serious than what
they are.
Fix those two issues together by not initializing pages in
RelationAddExtraPages() (but continue to do so in
RelationGetBufferForTuple(), which is linked much more closely to
heap), and accepting uninitialized pages as normal in
vacuumlazy.c. When vacuumlazy encounters an empty page it now adds it
to the FSM, but does nothing else. We chose to not issue a debug
message, much less a warning in that case - it seems rarely useful,
and quite likely to scare people unnecessarily.
For now empty pages aren't added to the VM, because standbys would not
re-discover such pages after a promotion. In contrast to other sources
for empty pages, there's no corresponding WAL records triggering FSM
updates during replay.
Previously when extending the relation, there was a moment between
extending the relation, and acquiring an exclusive lock on the new
page, in which another backend could lock the page. To avoid new
content being put on that new page, vacuumlazy needed to acquire the
extension lock for a brief moment when encountering a new page. A
second corner case, only working somewhat by accident, was that
RelationGetBufferForTuple() sometimes checks the last page in a
relation for free space, without consulting the FSM; that only worked
because PageGetHeapFreeSpace() interprets the zero page header in a
new page as no free space. The lack of handling this properly
required reverting the previous attempt in
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PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.