Script performing read-ahead on bitcoin's blockfiles

blk_ra.sh

#!/bin/bash
#
# blk_ra.sh - Script performing read-ahead on bitcoin's blockfiles
#
# In order to speed up data loading, this script performs read-ahead
# operations on the next block to be read by the bitcoin node.
#
# The expected setup for this speed-up to be effective is:
#
# - Blockchain index and chainstate database on SSD
# - Blocks on slow spindle storage
# - At least a coupls GB'sof available RAM for OS cache
#
# When doing initial data loading using a bootstrap file (after bootstrap.dat
# has been copied to blk*****.dat) or reindex operation, the bitcoin node
# will read each block in order. This script will ensure the next block
# is already cached in OS RAM then the node comes to read it.
#

trap 'echo "Error $? on line $LINENO"; exit 1' ERR

# process to look for... usually bitcoin-qt or bitcoind
PROC=bitcoin-qt

# Sleep time between runs - should be tuned as high as possible to avoid
# incurring extra load, but too high will miss some blocks
SLEEP=20

# Print debug messages (useful for tuning SLEEP, ensure each block is read at
# least 1-2 times)
DEBUG=1

while :
do
	# Get process pid
	bpid=$(pgrep -u$USER $PROC)
	[[ $bpid =~ ^[0-9]+$ ]] || { echo "Invalid or muiltiple pids found: '$bpid'";  false; }
	((DEBUG)) && echo -n "$PROC ($bpid): Looking for current block... "

	# This would be much more efficient using an LD_PRELOAD lib :(
	# Plus rely on likely inconsistent ls behavior!!
	while ! block=$(ls -lh /proc/$bpid/fd 2>/dev/null|grep 'blk[0-9]*\.dat')
	do
	       :
	done

	# Got full block path, split base and file names
	[[ $block =~ [[:space:]](/.*/)(blk[0-9]+\.dat) ]]
	base=${BASH_REMATCH[1]}
	block=${BASH_REMATCH[2]}
	((DEBUG)) && echo "Found! $block"

	# Get next block... Drop 0's or bash will assumes octal
	[[ $block =~ ^blk0*([0-9]+)\.dat ]]
	blkid=${BASH_REMATCH[1]}
	((++blkid))
	nextblk=$(printf "blk%05i.dat" $blkid)

	# Perform read-ahead
	((DEBUG)) && echo "Performing Read-Ahead on $nextblk"
	tcmd=""
	((DEBUG)) && tcmd="time"
	$tcmd schedtool -D -e cat "$base/$nextblk" >/dev/null

	sleep $SLEEP
done