Java tutorial
/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements. See the NOTICE file * distributed with this work for additional information * regarding copyright ownership. The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.hadoop.hbase.regionserver.wal; import java.util.ArrayList; import java.util.Collections; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Set; import java.util.TreeMap; import java.util.concurrent.ConcurrentMap; import java.util.concurrent.ConcurrentSkipListMap; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.hbase.HConstants; import org.apache.hadoop.hbase.util.Bytes; import com.google.common.collect.Maps; /** * Accounting of sequence ids per region and then by column family. So we can our accounting * current, call startCacheFlush and then finishedCacheFlush or abortCacheFlush so this instance * can keep abreast of the state of sequence id persistence. Also call update per append. */ class SequenceIdAccounting { private static final Log LOG = LogFactory.getLog(SequenceIdAccounting.class); /** * This lock ties all operations on {@link SequenceIdAccounting#flushingSequenceIds} and * {@link #lowestUnflushedSequenceIds} Maps. {@link #lowestUnflushedSequenceIds} has the * lowest outstanding sequence ids EXCEPT when flushing. When we flush, the current * lowest set for the region/column family are moved (atomically because of this lock) to * {@link #flushingSequenceIds}. * * <p>The two Maps are tied by this locking object EXCEPT when we go to update the lowest * entry; see {@link #lowest(byte[], Set, Long)}. In here is a putIfAbsent call on * {@link #lowestUnflushedSequenceIds}. In this latter case, we will add this lowest * sequence id if we find that there is no entry for the current column family. There will be no * entry only if we just came up OR we have moved aside current set of lowest sequence ids * because the current set are being flushed (by putting them into {@link #flushingSequenceIds}). * This is how we pick up the next 'lowest' sequence id per region per column family to be used * figuring what is in the next flush. */ private final Object tieLock = new Object(); /** * Map of encoded region names and family names to their OLDEST -- i.e. their first, * the longest-lived, their 'earliest', the 'lowest' -- sequence id. * * <p>When we flush, the current lowest sequence ids get cleared and added to * {@link #flushingSequenceIds}. The next append that comes in, is then added * here to {@link #lowestUnflushedSequenceIds} as the next lowest sequenceid. * * <p>If flush fails, currently server is aborted so no need to restore previous sequence ids. * <p>Needs to be concurrent Maps because we use putIfAbsent updating oldest. */ private final ConcurrentMap<byte[], ConcurrentMap<byte[], Long>> lowestUnflushedSequenceIds = new ConcurrentSkipListMap<byte[], ConcurrentMap<byte[], Long>>( Bytes.BYTES_COMPARATOR); /** * Map of encoded region names and family names to their lowest or OLDEST sequence/edit id * currently being flushed out to hfiles. Entries are moved here from * {@link #lowestUnflushedSequenceIds} while the lock {@link #tieLock} is held * (so movement between the Maps is atomic). */ private final Map<byte[], Map<byte[], Long>> flushingSequenceIds = new TreeMap<byte[], Map<byte[], Long>>( Bytes.BYTES_COMPARATOR); /** * Map of region encoded names to the latest/highest region sequence id. Updated on each * call to append. * <p> * This map uses byte[] as the key, and uses reference equality. It works in our use case as we * use {@link HRegionInfo#getEncodedNameAsBytes()} as keys. For a given region, it always returns * the same array. */ private Map<byte[], Long> highestSequenceIds = new HashMap<byte[], Long>(); /** * Returns the lowest unflushed sequence id for the region. * @param encodedRegionName * @return Lowest outstanding unflushed sequenceid for <code>encodedRegionName</code>. Will * return {@link HConstants#NO_SEQNUM} when none. */ long getLowestSequenceId(final byte[] encodedRegionName) { synchronized (this.tieLock) { Map<byte[], Long> m = this.flushingSequenceIds.get(encodedRegionName); long flushingLowest = m != null ? getLowestSequenceId(m) : Long.MAX_VALUE; m = this.lowestUnflushedSequenceIds.get(encodedRegionName); long unflushedLowest = m != null ? getLowestSequenceId(m) : HConstants.NO_SEQNUM; return Math.min(flushingLowest, unflushedLowest); } } /** * @param encodedRegionName * @param familyName * @return Lowest outstanding unflushed sequenceid for <code>encodedRegionname</code> and * <code>familyName</code>. Returned sequenceid may be for an edit currently being flushed. */ long getLowestSequenceId(final byte[] encodedRegionName, final byte[] familyName) { synchronized (this.tieLock) { Map<byte[], Long> m = this.flushingSequenceIds.get(encodedRegionName); if (m != null) { Long lowest = m.get(familyName); if (lowest != null) return lowest; } m = this.lowestUnflushedSequenceIds.get(encodedRegionName); if (m != null) { Long lowest = m.get(familyName); if (lowest != null) return lowest; } } return HConstants.NO_SEQNUM; } /** * Reset the accounting of highest sequenceid by regionname. * @return Return the previous accounting Map of regions to the last sequence id written into * each. */ Map<byte[], Long> resetHighest() { Map<byte[], Long> old = this.highestSequenceIds; this.highestSequenceIds = new HashMap<byte[], Long>(); return old; } /** * We've been passed a new sequenceid for the region. Set it as highest seen for this region and * if we are to record oldest, or lowest sequenceids, save it as oldest seen if nothing * currently older. * @param encodedRegionName * @param families * @param sequenceid * @param lowest Whether to keep running account of oldest sequence id. */ void update(byte[] encodedRegionName, Set<byte[]> families, long sequenceid, final boolean lowest) { Long l = Long.valueOf(sequenceid); this.highestSequenceIds.put(encodedRegionName, l); if (lowest) { ConcurrentMap<byte[], Long> m = getOrCreateLowestSequenceIds(encodedRegionName); for (byte[] familyName : families) { m.putIfAbsent(familyName, l); } } } ConcurrentMap<byte[], Long> getOrCreateLowestSequenceIds(byte[] encodedRegionName) { // Intentionally, this access is done outside of this.regionSequenceIdLock. Done per append. ConcurrentMap<byte[], Long> m = this.lowestUnflushedSequenceIds.get(encodedRegionName); if (m != null) return m; m = new ConcurrentSkipListMap<byte[], Long>(Bytes.BYTES_COMPARATOR); // Another thread may have added it ahead of us. ConcurrentMap<byte[], Long> alreadyPut = this.lowestUnflushedSequenceIds.putIfAbsent(encodedRegionName, m); return alreadyPut == null ? m : alreadyPut; } /** * @param sequenceids Map to search for lowest value. * @return Lowest value found in <code>sequenceids</code>. */ static long getLowestSequenceId(Map<byte[], Long> sequenceids) { long lowest = HConstants.NO_SEQNUM; for (Long sid : sequenceids.values()) { if (lowest == HConstants.NO_SEQNUM || sid.longValue() < lowest) { lowest = sid.longValue(); } } return lowest; } /** * @param src * @return New Map that has same keys as <code>src</code> but instead of a Map for a value, it * instead has found the smallest sequence id and it returns that as the value instead. */ private <T extends Map<byte[], Long>> Map<byte[], Long> flattenToLowestSequenceId(Map<byte[], T> src) { if (src == null || src.isEmpty()) return null; Map<byte[], Long> tgt = Maps.newHashMap(); for (Map.Entry<byte[], T> entry : src.entrySet()) { long lowestSeqId = getLowestSequenceId(entry.getValue()); if (lowestSeqId != HConstants.NO_SEQNUM) { tgt.put(entry.getKey(), lowestSeqId); } } return tgt; } /** * @param encodedRegionName Region to flush. * @param families Families to flush. May be a subset of all families in the region. * @return Returns {@link HConstants#NO_SEQNUM} if we are flushing the whole region OR if * we are flushing a subset of all families but there are no edits in those families not * being flushed; in other words, this is effectively same as a flush of all of the region * though we were passed a subset of regions. Otherwise, it returns the sequence id of the * oldest/lowest outstanding edit. */ Long startCacheFlush(final byte[] encodedRegionName, final Set<byte[]> families) { Map<byte[], Long> oldSequenceIds = null; Long lowestUnflushedInRegion = HConstants.NO_SEQNUM; synchronized (tieLock) { Map<byte[], Long> m = this.lowestUnflushedSequenceIds.get(encodedRegionName); if (m != null) { // NOTE: Removal from this.lowestUnflushedSequenceIds must be done in controlled // circumstance because another concurrent thread now may add sequenceids for this family // (see above in getOrCreateLowestSequenceId). Make sure you are ok with this. Usually it // is fine because updates are blocked when this method is called. Make sure!!! for (byte[] familyName : families) { Long seqId = m.remove(familyName); if (seqId != null) { if (oldSequenceIds == null) oldSequenceIds = Maps.newTreeMap(Bytes.BYTES_COMPARATOR); oldSequenceIds.put(familyName, seqId); } } if (oldSequenceIds != null && !oldSequenceIds.isEmpty()) { if (this.flushingSequenceIds.put(encodedRegionName, oldSequenceIds) != null) { LOG.warn("Flushing Map not cleaned up for " + Bytes.toString(encodedRegionName) + ", sequenceid=" + oldSequenceIds); } } if (m.isEmpty()) { // Remove it otherwise it will be in oldestUnflushedStoreSequenceIds for ever // even if the region is already moved to other server. // Do not worry about data racing, we held write lock of region when calling // startCacheFlush, so no one can add value to the map we removed. this.lowestUnflushedSequenceIds.remove(encodedRegionName); } else { // Flushing a subset of the region families. Return the sequence id of the oldest entry. lowestUnflushedInRegion = Collections.min(m.values()); } } } // Do this check outside lock. if (oldSequenceIds != null && oldSequenceIds.isEmpty()) { // TODO: if we have no oldStoreSeqNum, and WAL is not disabled, presumably either // the region is already flushing (which would make this call invalid), or there // were no appends after last flush, so why are we starting flush? Maybe we should // assert not empty. Less rigorous, but safer, alternative is telling the caller to stop. // For now preserve old logic. LOG.warn("Couldn't find oldest sequenceid for " + Bytes.toString(encodedRegionName)); } return lowestUnflushedInRegion; } void completeCacheFlush(final byte[] encodedRegionName) { synchronized (tieLock) { this.flushingSequenceIds.remove(encodedRegionName); } } void abortCacheFlush(final byte[] encodedRegionName) { // Method is called when we are crashing down because failed write flush AND it is called // if we fail prepare. The below is for the fail prepare case; we restore the old sequence ids. Map<byte[], Long> flushing = null; Map<byte[], Long> tmpMap = new TreeMap<byte[], Long>(Bytes.BYTES_COMPARATOR); // Here we are moving sequenceids from flushing back to unflushed; doing opposite of what // happened in startCacheFlush. During prepare phase, we have update lock on the region so // no edits should be coming in via append. synchronized (tieLock) { flushing = this.flushingSequenceIds.remove(encodedRegionName); if (flushing != null) { Map<byte[], Long> unflushed = getOrCreateLowestSequenceIds(encodedRegionName); for (Map.Entry<byte[], Long> e : flushing.entrySet()) { // Set into unflushed the 'old' oldest sequenceid and if any value in flushed with this // value, it will now be in tmpMap. tmpMap.put(e.getKey(), unflushed.put(e.getKey(), e.getValue())); } } } // Here we are doing some 'test' to see if edits are going in out of order. What is it for? // Carried over from old code. if (flushing != null) { for (Map.Entry<byte[], Long> e : flushing.entrySet()) { Long currentId = tmpMap.get(e.getKey()); if (currentId != null && currentId.longValue() <= e.getValue().longValue()) { String errorStr = Bytes.toString(encodedRegionName) + " family " + Bytes.toString(e.getKey()) + " acquired edits out of order current memstore seq=" + currentId + ", previous oldest unflushed id=" + e.getValue(); LOG.error(errorStr); Runtime.getRuntime().halt(1); } } } } /** * See if passed <code>sequenceids</code> are lower -- i.e. earlier -- than any outstanding * sequenceids, sequenceids we are holding on to in this accounting instance. * @param sequenceids Keyed by encoded region name. Cannot be null (doesn't make * sense for it to be null). * @return true if all sequenceids are lower, older than, the old sequenceids in this instance. */ boolean areAllLower(Map<byte[], Long> sequenceids) { Map<byte[], Long> flushing = null; Map<byte[], Long> unflushed = null; synchronized (this.tieLock) { // Get a flattened -- only the oldest sequenceid -- copy of current flushing and unflushed // data structures to use in tests below. flushing = flattenToLowestSequenceId(this.flushingSequenceIds); unflushed = flattenToLowestSequenceId(this.lowestUnflushedSequenceIds); } for (Map.Entry<byte[], Long> e : sequenceids.entrySet()) { long oldestFlushing = Long.MAX_VALUE; long oldestUnflushed = Long.MAX_VALUE; if (flushing != null) { if (flushing.containsKey(e.getKey())) oldestFlushing = flushing.get(e.getKey()); } if (unflushed != null) { if (unflushed.containsKey(e.getKey())) oldestUnflushed = unflushed.get(e.getKey()); } long min = Math.min(oldestFlushing, oldestUnflushed); if (min <= e.getValue()) return false; } return true; } /** * Iterates over the given Map and compares sequence ids with corresponding * entries in {@link #oldestUnflushedRegionSequenceIds}. If a region in * {@link #oldestUnflushedRegionSequenceIds} has a sequence id less than that passed * in <code>sequenceids</code> then return it. * @param sequenceids Sequenceids keyed by encoded region name. * @return regions found in this instance with sequence ids less than those passed in. */ byte[][] findLower(Map<byte[], Long> sequenceids) { List<byte[]> toFlush = null; // Keeping the old behavior of iterating unflushedSeqNums under oldestSeqNumsLock. synchronized (tieLock) { for (Map.Entry<byte[], Long> e : sequenceids.entrySet()) { Map<byte[], Long> m = this.lowestUnflushedSequenceIds.get(e.getKey()); if (m == null) continue; // The lowest sequence id outstanding for this region. long lowest = getLowestSequenceId(m); if (lowest != HConstants.NO_SEQNUM && lowest <= e.getValue()) { if (toFlush == null) toFlush = new ArrayList<byte[]>(); toFlush.add(e.getKey()); } } } return toFlush == null ? null : toFlush.toArray(new byte[][] { HConstants.EMPTY_BYTE_ARRAY }); } }