postgres

Alvaro Herrera f49a80c481 Fix "base" snapshot handling in logical decoding Two closely related bugs are fixed. First, xmin of logical slots was advanced too early. During xl_running_xacts processing, xmin of the slot was set to the oldest running xid in the record, but that's wrong: actually, snapshots which will be used for not-yet-replayed transactions might consider older txns as running too, so we need to keep xmin back for them. The problem wasn't noticed earlier because DDL which allows to delete tuple (set xmax) while some another not-yet-committed transaction looks at it is pretty rare, if not unique: e.g. all forms of ALTER TABLE which change schema acquire ACCESS EXCLUSIVE lock conflicting with any inserts. The included test case (test_decoding's oldest_xmin) uses ALTER of a composite type, which doesn't have such interlocking. To deal with this, we must be able to quickly retrieve oldest xmin (oldest running xid among all assigned snapshots) from ReorderBuffer. To fix, add another list of ReorderBufferTXNs to the reorderbuffer, where transactions are sorted by base-snapshot-LSN. This is slightly different from the existing (sorted by first-LSN) list, because a transaction can have an earlier LSN but a later Xmin, if its first record does not obtain an xmin (eg. xl_xact_assignment). Note this new list doesn't fully replace the existing txn list: we still need that one to prevent WAL recycling. The second issue concerns SnapBuilder snapshots and subtransactions. SnapBuildDistributeNewCatalogSnapshot never assigned a snapshot to a transaction that is known to be a subtxn, which is good in the common case that the top-level transaction already has one (no point in doing so), but a bug otherwise. To fix, arrange to transfer the snapshot from the subtxn to its top-level txn as soon as the kinship gets known. test_decoding's snapshot_transfer verifies this. Also, fix a minor memory leak: refcount of toplevel's old base snapshot was not decremented when the snapshot is transferred from child. Liberally sprinkle code comments, and rewrite a few existing ones. This part is my (Álvaro's) contribution to this commit, as I had to write all those comments in order to understand the existing code and Arseny's patch. Reported-by: Arseny Sher <a.sher@postgrespro.ru> Diagnosed-by: Arseny Sher <a.sher@postgrespro.ru> Co-authored-by: Arseny Sher <a.sher@postgrespro.ru> Co-authored-by: Álvaro Herrera <alvherre@alvh.no-ip.org> Reviewed-by: Antonin Houska <ah@cybertec.at> Discussion: https://postgr.es/m/87lgdyz1wj.fsf@ars-thinkpad		7 years ago
config	Update config.guess and config.sub	7 years ago
contrib	Fix "base" snapshot handling in logical decoding	7 years ago
doc	Fix upper limit for vacuum_cleanup_index_scale_factor	7 years ago
src	Fix "base" snapshot handling in logical decoding	7 years ago
.dir-locals.el	Make Emacs settings match perltidy configuration	7 years ago
.gitattributes	Remove contrib/tsearch2.	8 years ago
.gitignore	Support for optimizing and emitting code in LLVM JIT provider.	7 years ago
COPYRIGHT	Update copyright for 2018	8 years ago
GNUmakefile.in	Have "make coverage" recurse into contrib as well	9 years ago
HISTORY	Change documentation references to PG website to use https: not http:	8 years ago
Makefile	Fix non-GNU makefiles for AIX make.	8 years ago
README	Change documentation references to PG website to use https: not http:	8 years ago
README.git	Change documentation references to PG website to use https: not http:	8 years ago
aclocal.m4	Add configure infrastructure (--with-llvm) to enable LLVM support.	7 years ago
configure	Stamp 11beta2.	7 years ago
configure.in	Stamp 11beta2.	7 years ago

README

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
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