/** Tunes IO throttle when a new merge starts. */
private synchronized void updateIOThrottle(OneMerge newMerge) throws IOException {
if (doAutoIOThrottle == false) {
return;
}
double mergeMB = bytesToMB(newMerge.estimatedMergeBytes);
if (mergeMB < MIN_BIG_MERGE_MB) {
// Only watch non-trivial merges for throttling; this is safe because the MP must eventually
// have to do larger merges:
return;
}
long now = System.nanoTime();
// Simplistic closed-loop feedback control: if we find any other similarly
// sized merges running, then we are falling behind, so we bump up the
// IO throttle, else we lower it:
boolean newBacklog = isBacklog(now, newMerge);
boolean curBacklog = false;
if (newBacklog == false) {
if (mergeThreads.size() > maxThreadCount) {
// If there are already more than the maximum merge threads allowed, count that as backlog:
curBacklog = true;
} else {
// Now see if any still-running merges are backlog'd:
for (MergeThread mergeThread : mergeThreads) {
if (isBacklog(now, mergeThread.merge)) {
curBacklog = true;
break;
}
}
}
}
double curMBPerSec = targetMBPerSec;
if (newBacklog) {
// This new merge adds to the backlog: increase IO throttle by 20%
targetMBPerSec *= 1.20;
if (targetMBPerSec > MAX_MERGE_MB_PER_SEC) {
targetMBPerSec = MAX_MERGE_MB_PER_SEC;
}
if (verbose()) {
if (curMBPerSec == targetMBPerSec) {
message(
String.format(
Locale.ROOT,
"io throttle: new merge backlog; leave IO rate at ceiling %.1f MB/sec",
targetMBPerSec));
} else {
message(
String.format(
Locale.ROOT,
"io throttle: new merge backlog; increase IO rate to %.1f MB/sec",
targetMBPerSec));
}
}
} else if (curBacklog) {
// We still have an existing backlog; leave the rate as is:
if (verbose()) {
message(
String.format(
Locale.ROOT,
"io throttle: current merge backlog; leave IO rate at %.1f MB/sec",
targetMBPerSec));
}
} else {
// We are not falling behind: decrease IO throttle by 10%
targetMBPerSec /= 1.10;
if (targetMBPerSec < MIN_MERGE_MB_PER_SEC) {
targetMBPerSec = MIN_MERGE_MB_PER_SEC;
}
if (verbose()) {
if (curMBPerSec == targetMBPerSec) {
message(
String.format(
Locale.ROOT,
"io throttle: no merge backlog; leave IO rate at floor %.1f MB/sec",
targetMBPerSec));
} else {
message(
String.format(
Locale.ROOT,
"io throttle: no merge backlog; decrease IO rate to %.1f MB/sec",
targetMBPerSec));
}
}
}
double rate;
if (newMerge.maxNumSegments != -1) {
rate = forceMergeMBPerSec;
} else {
rate = targetMBPerSec;
}
newMerge.rateLimiter.setMBPerSec(rate);
targetMBPerSecChanged();
}
