Date: Wed, 22 Apr 2020 13:57:54 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Antonin Houska <ah@cybertec.at>
Cc: Andres Freund <andres@anarazel.de>,
	Michael Paquier <michael@paquier.xyz>, pgsql-hackers@postgresql.org
Subject: Re: 2pc leaks fds
Message-ID: <20200422175754.GA19858@alvherre.pgsql>
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Concretely, I propose to have a new struct like

typedef struct xlogReaderFuncs
{
	XLogPageReadCB read_page;
	XLogSegmentOpenCB open_segment;
	XLogSegmentCloseCB open_segment;
} xlogReaderFuncs;

#define XLOGREADER_FUNCS(...) &(xlogReaderFuncs){__VA_ARGS__}

and then invoke it something like

    xlogreader = XLogReaderAllocate(wal_segment_size, NULL,
                                    XLOGREADER_FUNCS(.readpage = &read_local_xlog_page,
                                              .opensegment = &wal_segment_open),
                                              .closesegment = &wal_segment_close),
                                    NULL);

(with suitable definitions for XLogSegmentOpenCB etc) so that the
support functions are all available at the xlogreader level, instead of
"open" being buried at the read-page level.  Any additional support
functions can be added easily.

This would give xlogreader a simpler interface.

If people like this, I could make this change for pg13 and avoid
changing the API again in pg14.

Thougths?

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services