diff options
| -rw-r--r-- | src/backend/storage/aio/read_stream.c | 81 |
1 files changed, 23 insertions, 58 deletions
diff --git a/src/backend/storage/aio/read_stream.c b/src/backend/storage/aio/read_stream.c index 74b9bae6313..a6c50b2ae24 100644 --- a/src/backend/storage/aio/read_stream.c +++ b/src/backend/storage/aio/read_stream.c @@ -117,13 +117,10 @@ struct ReadStream bool advice_enabled; /* - * Small buffer of block numbers, useful for 'ungetting' to resolve flow - * control problems when I/Os are split. Also useful for batch-loading - * block numbers in the fast path. + * One-block buffer to support 'ungetting' a block number, to resolve flow + * control problems when I/Os are split. */ - BlockNumber blocknums[16]; - int16 blocknums_count; - int16 blocknums_next; + BlockNumber buffered_blocknum; /* * The callback that will tell us which block numbers to read, and an @@ -167,23 +164,23 @@ get_per_buffer_data(ReadStream *stream, int16 buffer_index) } /* - * Ask the callback which block it would like us to read next, with a small - * buffer in front to allow read_stream_unget_block() to work and to allow the - * fast path to skip this function and work directly from the array. + * Ask the callback which block it would like us to read next, with a one block + * buffer in front to allow read_stream_unget_block() to work. */ static inline BlockNumber read_stream_get_block(ReadStream *stream, void *per_buffer_data) { - if (stream->blocknums_next < stream->blocknums_count) - return stream->blocknums[stream->blocknums_next++]; + BlockNumber blocknum; - /* - * We only bother to fetch one at a time here (but see the fast path which - * uses more). - */ - return stream->callback(stream, - stream->callback_private_data, - per_buffer_data); + blocknum = stream->buffered_blocknum; + if (blocknum != InvalidBlockNumber) + stream->buffered_blocknum = InvalidBlockNumber; + else + blocknum = stream->callback(stream, + stream->callback_private_data, + per_buffer_data); + + return blocknum; } /* @@ -193,42 +190,12 @@ read_stream_get_block(ReadStream *stream, void *per_buffer_data) static inline void read_stream_unget_block(ReadStream *stream, BlockNumber blocknum) { - if (stream->blocknums_next == stream->blocknums_count) - { - /* Never initialized or entirely consumed. Re-initialize. */ - stream->blocknums[0] = blocknum; - stream->blocknums_count = 1; - stream->blocknums_next = 0; - } - else - { - /* Must be the last value return from blocknums array. */ - Assert(stream->blocknums_next > 0); - stream->blocknums_next--; - Assert(stream->blocknums[stream->blocknums_next] == blocknum); - } + /* We shouldn't ever unget more than one block. */ + Assert(stream->buffered_blocknum == InvalidBlockNumber); + Assert(blocknum != InvalidBlockNumber); + stream->buffered_blocknum = blocknum; } -#ifndef READ_STREAM_DISABLE_FAST_PATH -static void -read_stream_fill_blocknums(ReadStream *stream) -{ - BlockNumber blocknum; - int i = 0; - - do - { - blocknum = stream->callback(stream, - stream->callback_private_data, - NULL); - stream->blocknums[i++] = blocknum; - } while (i < lengthof(stream->blocknums) && - blocknum != InvalidBlockNumber); - stream->blocknums_count = i; - stream->blocknums_next = 0; -} -#endif - static void read_stream_start_pending_read(ReadStream *stream, bool suppress_advice) { @@ -531,6 +498,7 @@ read_stream_begin_relation(int flags, stream->queue_size = queue_size; stream->callback = callback; stream->callback_private_data = callback_private_data; + stream->buffered_blocknum = InvalidBlockNumber; /* * Skip the initial ramp-up phase if the caller says we're going to be @@ -601,9 +569,7 @@ read_stream_next_buffer(ReadStream *stream, void **per_buffer_data) Assert(buffer != InvalidBuffer); /* Choose the next block to pin. */ - if (unlikely(stream->blocknums_next == stream->blocknums_count)) - read_stream_fill_blocknums(stream); - next_blocknum = stream->blocknums[stream->blocknums_next++]; + next_blocknum = read_stream_get_block(stream, NULL); if (likely(next_blocknum != InvalidBlockNumber)) { @@ -779,9 +745,8 @@ read_stream_reset(ReadStream *stream) /* Stop looking ahead. */ stream->distance = 0; - /* Forget buffered block numbers and fast path state. */ - stream->blocknums_next = 0; - stream->blocknums_count = 0; + /* Forget buffered block number and fast path state. */ + stream->buffered_blocknum = InvalidBlockNumber; stream->fast_path = false; /* Unpin anything that wasn't consumed. */ |