Use streaming I/O in pg_prewarm.

Instead of calling ReadBuffer() repeatedly, use the new streaming
interface.  This commit provides a very simple example of such a
transformation.

Discussion: https://postgr.es/m/CA+hUKGJkOiOCa+mag4BF+zHo7qo=o9CFheB8=g6uT5TUm2gkvA@mail.gmail.com

diff --git a/contrib/pg_prewarm/pg_prewarm.c b/contrib/pg_prewarm/pg_prewarm.c
index 8541e4d6e46162a73bd0b495e4158ce66d4b1288..5c859e983c5cac6266e84bd85521ca33bec014bd 100644 (file)
--- a/contrib/pg_prewarm/pg_prewarm.c
+++ b/contrib/pg_prewarm/pg_prewarm.c
@@ -19,6 +19,7 @@
 #include "fmgr.h"
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
+#include "storage/read_stream.h"
 #include "storage/smgr.h"
 #include "utils/acl.h"
 #include "utils/builtins.h"
@@ -38,6 +39,25 @@ typedef enum
 
 static PGIOAlignedBlock blockbuffer;
 
+struct pg_prewarm_read_stream_private
+{
+   BlockNumber blocknum;
+   int64       last_block;
+};
+
+static BlockNumber
+pg_prewarm_read_stream_next_block(ReadStream *stream,
+                                 void *callback_private_data,
+                                 void *per_buffer_data)
+{
+   struct pg_prewarm_read_stream_private *p = callback_private_data;
+
+   if (p->blocknum <= p->last_block)
+       return p->blocknum++;
+
+   return InvalidBlockNumber;
+}
+
 /*
  * pg_prewarm(regclass, mode text, fork text,
  *           first_block int8, last_block int8)
@@ -183,18 +203,36 @@ pg_prewarm(PG_FUNCTION_ARGS)
    }
    else if (ptype == PREWARM_BUFFER)
    {
+       struct pg_prewarm_read_stream_private p;
+       ReadStream *stream;
+
        /*
         * In buffer mode, we actually pull the data into shared_buffers.
         */
+
+       /* Set up the private state for our streaming buffer read callback. */
+       p.blocknum = first_block;
+       p.last_block = last_block;
+
+       stream = read_stream_begin_relation(READ_STREAM_FULL,
+                                           NULL,
+                                           rel,
+                                           forkNumber,
+                                           pg_prewarm_read_stream_next_block,
+                                           &p,
+                                           0);
+
        for (block = first_block; block <= last_block; ++block)
        {
            Buffer      buf;
 
            CHECK_FOR_INTERRUPTS();
-           buf = ReadBufferExtended(rel, forkNumber, block, RBM_NORMAL, NULL);
+           buf = read_stream_next_buffer(stream, NULL);
            ReleaseBuffer(buf);
            ++blocks_done;
        }
+       Assert(read_stream_next_buffer(stream, NULL) == InvalidBuffer);
+       read_stream_end(stream);
    }
 
    /* Close relation, release lock. */