Add circular WAL decoding buffer.
Teach xlogreader.c to decode its output into a circular buffer, to
support optimizations based on looking ahead.
* XLogReadRecord() works as before, consuming records one by one, and
allowing them to be examined via the traditional XLogRecGetXXX()
macros.
* An alternative new interface XLogNextRecord() is added that returns
pointers to DecodedXLogRecord structs that can be examined directly.
* XLogReadAhead() provides a second cursor that lets you see
further ahead, as long as data is available and there is enough space
in the decoding buffer. This returns DecodedXLogRecord pointers to the
caller, but also adds them to a queue of records that will later be
consumed by XLogNextRecord()/XLogReadRecord().
The buffer's size is controlled with wal_decode_buffer_size. The buffer
could potentially be placed into shared memory, for future projects.
Large records that don't fit in the circular buffer are called
"oversized" and allocated separately with palloc().
Discussion: https://postgr.es/m/CA+hUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq=AovOddfHpA@mail.gmail.com
Branch
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master
Details
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https://git.postgresql.org/pg/commitdiff/f003d9f8721b3249e4aec8a1946034579d40d42c
Modified Files
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src/backend/access/transam/generic_xlog.c | 6 +-
src/backend/access/transam/xlog.c | 28 +-
src/backend/access/transam/xlogreader.c | 744 ++++++++++++++++++++++++------
src/backend/access/transam/xlogutils.c | 2 +-
src/backend/replication/logical/decode.c | 2 +-
src/bin/pg_rewind/parsexlog.c | 2 +-
src/bin/pg_waldump/pg_waldump.c | 22 +-
src/include/access/xlogreader.h | 128 +++--
8 files changed, 734 insertions(+), 200 deletions(-)