bool
BgBufferSync(void)
{                                ……
    int            bufs_to_lap;                ……                            if (saved_info_valid)                            {        //added by gaojian        fprintf(stderr,"saved_info_valid true\n");                            int32        passes_delta = strategy_passes - prev_strategy_passes;                                        strategy_delta = strategy_buf_id - prev_strategy_buf_id;                        strategy_delta += (long) passes_delta *NBuffers;           ......
        if ((int32) (next_passes - strategy_passes) > 0)                        {                                    fprintf(stderr,"next_pass > strategy_passes.\n");/* we're one pass ahead of the strategy point */                    bufs_to_lap = strategy_buf_id - next_to_clean;                    ……                    }                        else if (next_passes == strategy_passes &&                        next_to_clean >= strategy_buf_id)                {            fprintf(stderr,"next_passes == strategy_passes.\n");                         /* on same pass, but ahead or at least not behind */                    bufs_to_lap = NBuffers - (next_to_clean - strategy_buf_id);                    ……                    }                        else                        {                        fprintf(stderr,"we are behind.\n"); /*                    * We're behind, so skip forward to the strategy point and start                    * cleaning from there.                    */                    next_to_clean = strategy_buf_id;                    next_passes = strategy_passes;                    bufs_to_lap = NBuffers;                    ……                    }                 }                            else                            {          fprintf(stderr,"saved_info_valid false\n");                          ……                        bufs_to_lap = NBuffers;                        }                            ……
    bufs_ahead = NBuffers - bufs_to_lap;                            ……
    num_to_scan = bufs_to_lap;     ......
    /* Execute the LRU scan */                            while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est)                            {                            //added by gaojian                        fprintf(stderr,"num_to_scan is: %d \n",num_to_scan);                        int    buffer_state = SyncOneBuffer(next_to_clean, true);                    if (++next_to_clean >= NBuffers)                        {                        next_to_clean = 0;           elog(INFO,"------------------next_passes++.\n");                    next_passes++;                    }                        num_to_scan--;                        ……                        }
    ……                            new_strategy_delta = bufs_to_lap - num_to_scan;                            new_recent_alloc = reusable_buffers - reusable_buffers_est;                            if (new_strategy_delta > 0 && new_recent_alloc > 0)                            {                            scans_per_alloc = (float) new_strategy_delta / (float) new_recent_alloc;                        smoothed_density += (scans_per_alloc - smoothed_density) /                        smoothing_samples;                    ……                        }    ......
}                                

[postgres@localhost bin]$ ./postgres -D /usr/local/pgsql/data
LOG:  database system was shut down at 2012-11-02 13:51:46 CST
saved_info_valid false.
LOG:  autovacuum launcher started
LOG:  database system is ready to accept connections
saved_info_valid true.
next_passes == strategy_passes.
saved_info_valid true.
next_passes == strategy_passes.
saved_info_valid true.
next_passes == strategy_passes.
saved_info_valid true.
next_passes == strategy_passes.
saved_info_valid true.
......