From 6c3ea233758ae12784b716861a29e0ce5a39cb79 Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Tue, 25 Mar 2025 14:02:44 +1300 Subject: [PATCH] fixup to v2.12-0010 This gives io_concurrency=0 the expected meaning for AIO, namely "no concurrency, just use synchronous I/O". --- src/backend/storage/aio/read_stream.c | 30 +++++++++++++++------------ 1 file changed, 17 insertions(+), 13 deletions(-) diff --git a/src/backend/storage/aio/read_stream.c b/src/backend/storage/aio/read_stream.c index 039d7dc71a5..cec93129f58 100644 --- a/src/backend/storage/aio/read_stream.c +++ b/src/backend/storage/aio/read_stream.c @@ -100,6 +100,7 @@ struct ReadStream int16 pinned_buffers; int16 distance; int16 initialized_buffers; + int read_buffers_flags; bool sync_mode; /* using io_method=sync */ bool batch_mode; /* READ_STREAM_USE_BATCHING */ bool advice_enabled; @@ -253,7 +254,7 @@ read_stream_start_pending_read(ReadStream *stream) Assert(stream->next_buffer_index == stream->oldest_buffer_index); /* Do we need to issue read-ahead advice? */ - flags = 0; + flags = stream->read_buffers_flags; if (stream->advice_enabled) { if (stream->pending_read_blocknum == stream->seq_blocknum) @@ -264,7 +265,7 @@ read_stream_start_pending_read(ReadStream *stream) * then stay of the way of the kernel's own read-ahead. */ if (stream->seq_until_processed != InvalidBlockNumber) - flags = READ_BUFFERS_ISSUE_ADVICE; + flags |= READ_BUFFERS_ISSUE_ADVICE; } else { @@ -275,7 +276,7 @@ read_stream_start_pending_read(ReadStream *stream) */ stream->seq_until_processed = stream->pending_read_blocknum; if (stream->pinned_buffers > 0) - flags = READ_BUFFERS_ISSUE_ADVICE; + flags |= READ_BUFFERS_ISSUE_ADVICE; } } @@ -660,8 +661,7 @@ read_stream_begin_impl(int flags, #ifdef USE_PREFETCH /* - * This system supports prefetching advice. - * + * Read-ahead advice simulating asynchronous I/O with synchronous calls. * Issue advice only if AIO is not used, direct I/O isn't enabled, the * caller hasn't promised sequential access (overriding our detection * heuristics), and max_ios hasn't been set to zero. @@ -674,15 +674,15 @@ read_stream_begin_impl(int flags, #endif /* - * For now, max_ios = 0 is interpreted as max_ios = 1 with advice disabled - * above. If we had real asynchronous I/O we might need a slightly - * different definition. - * - * FIXME: Not sure what different definition we would need? I guess we - * could add the READ_BUFFERS_SYNCHRONOUSLY flag automatically? + * Setting max_ios to zero disables AIO and advice-based pseudo AIO, but + * we still need to allocate space to combine and run one I/O. Bump it up + * to one, and remember to ask for synchronous I/O only. */ if (max_ios == 0) + { max_ios = 1; + stream->read_buffers_flags = READ_BUFFERS_SYNCHRONOUSLY; + } /* * Capture stable values for these two GUC-derived numbers for the @@ -826,6 +826,11 @@ read_stream_next_buffer(ReadStream *stream, void **per_buffer_data) if (likely(next_blocknum != InvalidBlockNumber)) { + int flags = stream->read_buffers_flags; + + if (stream->advice_enabled) + flags |= READ_BUFFERS_ISSUE_ADVICE; + /* * Pin a buffer for the next call. Same buffer entry, and * arbitrary I/O entry (they're all free). We don't have to @@ -841,8 +846,7 @@ read_stream_next_buffer(ReadStream *stream, void **per_buffer_data) if (likely(!StartReadBuffer(&stream->ios[0].op, &stream->buffers[oldest_buffer_index], next_blocknum, - stream->advice_enabled ? - READ_BUFFERS_ISSUE_ADVICE : 0))) + flags))) { /* Fast return. */ return buffer; -- 2.48.1