Rationalize parallel dump/restore's handling of worker cmd/status messages

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 27 September 2016 12:56 UTC

The existing APIs for creating and parsing command and status messages are rather messy; for example, archive-format modules have to provide code for constructing command messages, which is entirely pointless since the code to read them is hard-wired in WaitForCommands() and hence no format-specific variation is actually possible. But there's little foreseeable reason to need format-specific variation anyway.

The situation for status messages is no better; at least those are both constructed and parsed by format-specific code, but said code is quite redundant since there's no actual need for format-specific variation.

To add insult to injury, the first API involves returning pointers to static buffers, which is bad, while the second involves returning pointers to malloc'd strings, which is safer but randomly inconsistent.

Hence, get rid of the MasterStartParallelItem and MasterEndParallelItem APIs, and instead write centralized functions that construct and parse command and status messages. If we ever do need more flexibility, these functions can be the standard implementations of format-specific callback methods, but that's a long way off if it ever happens.

Tom Lane, reviewed by Kevin Grittner

Discussion: <17340.1464465717@sss.pgh.pa.us>

fb03d08 Rationalize parallel dump/restore's handling of worker cmd/status messages.
src/bin/pg_dump/parallel.c | 232 ++++++++++++++++++++-------------
src/bin/pg_dump/pg_backup_archiver.h | 11 +-
src/bin/pg_dump/pg_backup_custom.c | 75 +----------
src/bin/pg_dump/pg_backup_directory.c | 115 ++--------------
src/bin/pg_dump/pg_backup_tar.c | 3 -
5 files changed, 162 insertions(+), 274 deletions(-)

Upstream: git.postgresql.org

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