read_stream.h File Reference

#include "storage/bufmgr.h"
#include "storage/smgr.h"

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Macros
#define	READ_STREAM_DEFAULT   0x00
#define	READ_STREAM_MAINTENANCE   0x01
#define	READ_STREAM_SEQUENTIAL   0x02
#define	READ_STREAM_FULL   0x04

Typedefs
typedef struct ReadStream	ReadStream
typedef BlockNumber(*	ReadStreamBlockNumberCB) (ReadStream *stream, void *callback_private_data, void *per_buffer_data)

Functions
ReadStream *	read_stream_begin_relation (int flags, BufferAccessStrategy strategy, Relation rel, ForkNumber forknum, ReadStreamBlockNumberCB callback, void *callback_private_data, size_t per_buffer_data_size)
Buffer	read_stream_next_buffer (ReadStream *stream, void **per_buffer_data)
ReadStream *	read_stream_begin_smgr_relation (int flags, BufferAccessStrategy strategy, SMgrRelation smgr, char smgr_persistence, ForkNumber forknum, ReadStreamBlockNumberCB callback, void *callback_private_data, size_t per_buffer_data_size)
void	read_stream_reset (ReadStream *stream)
void	read_stream_end (ReadStream *stream)

Macro Definition Documentation

READ_STREAM_DEFAULT

#define READ_STREAM_DEFAULT   0x00

Definition at line 21 of file read_stream.h.

READ_STREAM_FULL

#define READ_STREAM_FULL   0x04

Definition at line 43 of file read_stream.h.

READ_STREAM_MAINTENANCE

#define READ_STREAM_MAINTENANCE   0x01

Definition at line 28 of file read_stream.h.

READ_STREAM_SEQUENTIAL

#define READ_STREAM_SEQUENTIAL   0x02

Definition at line 36 of file read_stream.h.

Typedef Documentation

ReadStream

typedef struct ReadStream ReadStream

Definition at line 1 of file read_stream.h.

ReadStreamBlockNumberCB

typedef BlockNumber(* ReadStreamBlockNumberCB) (ReadStream *stream, void *callback_private_data, void *per_buffer_data)

Definition at line 49 of file read_stream.h.

Function Documentation

read_stream_begin_relation()

ReadStream* read_stream_begin_relation	(	int	flags,
		BufferAccessStrategy	strategy,
		Relation	rel,
		ForkNumber	forknum,
		ReadStreamBlockNumberCB	callback,
		void *	callback_private_data,
		size_t	per_buffer_data_size
	)

Definition at line 566 of file read_stream.c.

{
    return read_stream_begin_impl(flags,
                                  strategy,
                                  rel,
                                  RelationGetSmgr(rel),
                                  rel->rd_rel->relpersistence,
                                  forknum,
                                  callback,
                                  callback_private_data,
                                  per_buffer_data_size);
}

References callback(), RelationData::rd_rel, read_stream_begin_impl(), and RelationGetSmgr().

Referenced by acquire_sample_rows(), heap_beginscan(), and pg_prewarm().

read_stream_begin_smgr_relation()

ReadStream* read_stream_begin_smgr_relation	(	int	flags,
		BufferAccessStrategy	strategy,
		SMgrRelation	smgr,
		char	smgr_persistence,
		ForkNumber	forknum,
		ReadStreamBlockNumberCB	callback,
		void *	callback_private_data,
		size_t	per_buffer_data_size
	)

Definition at line 590 of file read_stream.c.

{
    return read_stream_begin_impl(flags,
                                  strategy,
                                  NULL,
                                  smgr,
                                  smgr_persistence,
                                  forknum,
                                  callback,
                                  callback_private_data,
                                  per_buffer_data_size);
}

References callback(), and read_stream_begin_impl().

Referenced by RelationCopyStorageUsingBuffer().

read_stream_end()

void read_stream_end

(

ReadStream *

stream

)

Definition at line 850 of file read_stream.c.

{
    read_stream_reset(stream);
    pfree(stream);
}

References pfree(), and read_stream_reset().

Referenced by acquire_sample_rows(), heap_endscan(), pg_prewarm(), and RelationCopyStorageUsingBuffer().

read_stream_next_buffer()

Buffer read_stream_next_buffer	(	ReadStream *	stream,
		void **	per_buffer_data
	)

Definition at line 620 of file read_stream.c.

{
    Buffer      buffer;
    int16       oldest_buffer_index;
 
#ifndef READ_STREAM_DISABLE_FAST_PATH
 
    /*
     * A fast path for all-cached scans (behavior A).  This is the same as the
     * usual algorithm, but it is specialized for no I/O and no per-buffer
     * data, so we can skip the queue management code, stay in the same buffer
     * slot and use singular StartReadBuffer().
     */
    if (likely(stream->fast_path))
    {
        BlockNumber next_blocknum;
 
        /* Fast path assumptions. */
        Assert(stream->ios_in_progress == 0);
        Assert(stream->pinned_buffers == 1);
        Assert(stream->distance == 1);
        Assert(stream->pending_read_nblocks == 0);
        Assert(stream->per_buffer_data_size == 0);
 
        /* We're going to return the buffer we pinned last time. */
        oldest_buffer_index = stream->oldest_buffer_index;
        Assert((oldest_buffer_index + 1) % stream->queue_size ==
               stream->next_buffer_index);
        buffer = stream->buffers[oldest_buffer_index];
        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++];
 
        if (likely(next_blocknum != InvalidBlockNumber))
        {
            /*
             * Pin a buffer for the next call.  Same buffer entry, and
             * arbitrary I/O entry (they're all free).  We don't have to
             * adjust pinned_buffers because we're transferring one to caller
             * but pinning one more.
             */
            if (likely(!StartReadBuffer(&stream->ios[0].op,
                                        &stream->buffers[oldest_buffer_index],
                                        next_blocknum,
                                        stream->advice_enabled ?
                                        READ_BUFFERS_ISSUE_ADVICE : 0)))
            {
                /* Fast return. */
                return buffer;
            }
 
            /* Next call must wait for I/O for the newly pinned buffer. */
            stream->oldest_io_index = 0;
            stream->next_io_index = stream->max_ios > 1 ? 1 : 0;
            stream->ios_in_progress = 1;
            stream->ios[0].buffer_index = oldest_buffer_index;
            stream->seq_blocknum = next_blocknum + 1;
        }
        else
        {
            /* No more blocks, end of stream. */
            stream->distance = 0;
            stream->oldest_buffer_index = stream->next_buffer_index;
            stream->pinned_buffers = 0;
        }
 
        stream->fast_path = false;
        return buffer;
    }
#endif
 
    if (unlikely(stream->pinned_buffers == 0))
    {
        Assert(stream->oldest_buffer_index == stream->next_buffer_index);
 
        /* End of stream reached?  */
        if (stream->distance == 0)
            return InvalidBuffer;
 
        /*
         * The usual order of operations is that we look ahead at the bottom
         * of this function after potentially finishing an I/O and making
         * space for more, but if we're just starting up we'll need to crank
         * the handle to get started.
         */
        read_stream_look_ahead(stream, true);
 
        /* End of stream reached? */
        if (stream->pinned_buffers == 0)
        {
            Assert(stream->distance == 0);
            return InvalidBuffer;
        }
    }
 
    /* Grab the oldest pinned buffer and associated per-buffer data. */
    Assert(stream->pinned_buffers > 0);
    oldest_buffer_index = stream->oldest_buffer_index;
    Assert(oldest_buffer_index >= 0 &&
           oldest_buffer_index < stream->queue_size);
    buffer = stream->buffers[oldest_buffer_index];
    if (per_buffer_data)
        *per_buffer_data = get_per_buffer_data(stream, oldest_buffer_index);
 
    Assert(BufferIsValid(buffer));
 
    /* Do we have to wait for an associated I/O first? */
    if (stream->ios_in_progress > 0 &&
        stream->ios[stream->oldest_io_index].buffer_index == oldest_buffer_index)
    {
        int16       io_index = stream->oldest_io_index;
        int16       distance;
 
        /* Sanity check that we still agree on the buffers. */
        Assert(stream->ios[io_index].op.buffers ==
               &stream->buffers[oldest_buffer_index]);
 
        WaitReadBuffers(&stream->ios[io_index].op);
 
        Assert(stream->ios_in_progress > 0);
        stream->ios_in_progress--;
        if (++stream->oldest_io_index == stream->max_ios)
            stream->oldest_io_index = 0;
 
        if (stream->ios[io_index].op.flags & READ_BUFFERS_ISSUE_ADVICE)
        {
            /* Distance ramps up fast (behavior C). */
            distance = stream->distance * 2;
            distance = Min(distance, stream->max_pinned_buffers);
            stream->distance = distance;
        }
        else
        {
            /* No advice; move towards io_combine_limit (behavior B). */
            if (stream->distance > io_combine_limit)
            {
                stream->distance--;
            }
            else
            {
                distance = stream->distance * 2;
                distance = Min(distance, io_combine_limit);
                distance = Min(distance, stream->max_pinned_buffers);
                stream->distance = distance;
            }
        }
    }
 
#ifdef CLOBBER_FREED_MEMORY
    /* Clobber old buffer and per-buffer data for debugging purposes. */
    stream->buffers[oldest_buffer_index] = InvalidBuffer;
 
    /*
     * The caller will get access to the per-buffer data, until the next call.
     * We wipe the one before, which is never occupied because queue_size
     * allowed one extra element.  This will hopefully trip up client code
     * that is holding a dangling pointer to it.
     */
    if (stream->per_buffer_data)
        wipe_mem(get_per_buffer_data(stream,
                                     oldest_buffer_index == 0 ?
                                     stream->queue_size - 1 :
                                     oldest_buffer_index - 1),
                 stream->per_buffer_data_size);
#endif
 
    /* Pin transferred to caller. */
    Assert(stream->pinned_buffers > 0);
    stream->pinned_buffers--;
 
    /* Advance oldest buffer, with wrap-around. */
    stream->oldest_buffer_index++;
    if (stream->oldest_buffer_index == stream->queue_size)
        stream->oldest_buffer_index = 0;
 
    /* Prepare for the next call. */
    read_stream_look_ahead(stream, false);
 
#ifndef READ_STREAM_DISABLE_FAST_PATH
    /* See if we can take the fast path for all-cached scans next time. */
    if (stream->ios_in_progress == 0 &&
        stream->pinned_buffers == 1 &&
        stream->distance == 1 &&
        stream->pending_read_nblocks == 0 &&
        stream->per_buffer_data_size == 0)
    {
        stream->fast_path = true;
    }
#endif
 
    return buffer;
}

References ReadStream::advice_enabled, Assert, ReadStream::blocknums, ReadStream::blocknums_count, ReadStream::blocknums_next, InProgressIO::buffer_index, BufferIsValid(), ReadStream::buffers, ReadBuffersOperation::buffers, ReadStream::distance, ReadStream::fast_path, ReadBuffersOperation::flags, get_per_buffer_data(), InvalidBlockNumber, InvalidBuffer, io_combine_limit, ReadStream::ios, ReadStream::ios_in_progress, likely, ReadStream::max_ios, ReadStream::max_pinned_buffers, Min, ReadStream::next_buffer_index, ReadStream::next_io_index, ReadStream::oldest_buffer_index, ReadStream::oldest_io_index, InProgressIO::op, ReadStream::pending_read_nblocks, ReadStream::per_buffer_data, ReadStream::per_buffer_data_size, ReadStream::pinned_buffers, ReadStream::queue_size, READ_BUFFERS_ISSUE_ADVICE, read_stream_fill_blocknums(), read_stream_look_ahead(), ReadStream::seq_blocknum, StartReadBuffer(), unlikely, and WaitReadBuffers().

Referenced by heap_fetch_next_buffer(), heapam_scan_analyze_next_block(), pg_prewarm(), read_stream_reset(), and RelationCopyStorageUsingBuffer().

read_stream_reset()

void read_stream_reset

(

ReadStream *

stream

)

Definition at line 823 of file read_stream.c.

{
    Buffer      buffer;
 
    /* Stop looking ahead. */
    stream->distance = 0;
 
    /* Forget buffered block numbers and fast path state. */
    stream->blocknums_next = 0;
    stream->blocknums_count = 0;
    stream->fast_path = false;
 
    /* Unpin anything that wasn't consumed. */
    while ((buffer = read_stream_next_buffer(stream, NULL)) != InvalidBuffer)
        ReleaseBuffer(buffer);
 
    Assert(stream->pinned_buffers == 0);
    Assert(stream->ios_in_progress == 0);
 
    /* Start off assuming data is cached. */
    stream->distance = 1;
}

References Assert, ReadStream::blocknums_count, ReadStream::blocknums_next, ReadStream::distance, ReadStream::fast_path, InvalidBuffer, ReadStream::ios_in_progress, ReadStream::pinned_buffers, read_stream_next_buffer(), and ReleaseBuffer().

Referenced by heap_fetch_next_buffer(), heap_rescan(), and read_stream_end().