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這篇文章主要為大家展示了“HBase compaction有什么用”,內(nèi)容簡(jiǎn)而易懂,條理清晰,希望能夠幫助大家解決疑惑,下面讓小編帶領(lǐng)大家一起研究并學(xué)習(xí)一下“HBase compaction有什么用”這篇文章吧。
compaction是將多個(gè)HFile合并為一個(gè)HFile操作,
進(jìn)行compaction有如下幾個(gè)作用:
減少HFile文件的個(gè)數(shù),
HFile減少可能提高讀取性能,
清除過期和刪除數(shù)據(jù)。
compaction有二種類型:minor 和 major
1)Minor操作只用來做部分文件的合并操作以及包括minVersion=0并且設(shè)置ttl的過期版本清理,不做任何刪除數(shù)據(jù)、多版本數(shù)據(jù)的清理工作。
2)Major操作是對(duì)Region下的HStore下的所有StoreFile執(zhí)行合并操作,會(huì)做刪除數(shù)據(jù),多版本數(shù)據(jù)清理工作,最終的結(jié)果是整理合并出一個(gè)文件。
HRegionServer在啟動(dòng)的時(shí)候,會(huì)啟動(dòng)compactionChecker線程,compactionChecker會(huì)檢測(cè)region是否需要compaction。
主要執(zhí)行的邏輯如下:
protected void chore() { for (HRegion r : this.instance.onlineRegions.values()) { if (r == null) continue; for (Store s : r.getStores().values()) { try { long multiplier = s.getCompactionCheckMultiplier(); assert multiplier > 0; if (iteration % multiplier != 0) continue; if (s.needsCompaction()) { // Queue a compaction. Will recognize if major is needed. this.instance.compactSplitThread.requestSystemCompaction(r, s, getName() + " requests compaction"); } else if (s.isMajorCompaction()) { if (majorCompactPriority == DEFAULT_PRIORITY || majorCompactPriority > r.getCompactPriority()) { this.instance.compactSplitThread.requestCompaction(r, s, getName() + " requests major compaction; use default priority", null); } else { this.instance.compactSplitThread.requestCompaction(r, s, getName() + " requests major compaction; use configured priority", this.majorCompactPriority, null); } } } catch (IOException e) { LOG.warn("Failed major compaction check on " + r, e); } } } iteration = (iteration == Long.MAX_VALUE) ? 0 : (iteration + 1); } }
如代碼,遍歷onlineRegions,獲取每個(gè)region的Store進(jìn)行判斷,其中needsCompaction邏輯如下:
public boolean needsCompaction(final Collection<StoreFile> storeFiles, final List<StoreFile> filesCompacting) { int numCandidates = storeFiles.size() - filesCompacting.size(); return numCandidates >= comConf.getMinFilesToCompact(); }
minFilesToCompact由hbase.hstore.compaction.min(老版本是:hbase.hstore.compactionThreshold)控制,默認(rèn)值為3,即store下面的storeFiles數(shù)量 減去 正在compaction的數(shù)量 >=3是,需要做compaction。
needsCompaction為true后,會(huì)調(diào)用compactSplitThread.requestSystemCompaction方法,發(fā)送compaction請(qǐng)求,具體內(nèi)容會(huì)在compactSplitThread線程里分析。
needsCompaction為false后,會(huì)判斷是否為isMajorCompaction,具體邏輯如下:
/* * @param filesToCompact Files to compact. Can be null. * @return True if we should run a major compaction. */ public boolean isMajorCompaction(final Collection<StoreFile> filesToCompact) throws IOException { boolean result = false; long mcTime = getNextMajorCompactTime(filesToCompact); if (filesToCompact == null || filesToCompact.isEmpty() || mcTime == 0) { return result; } // TODO: Use better method for determining stamp of last major (HBASE-2990) long lowTimestamp = StoreUtils.getLowestTimestamp(filesToCompact); long now = System.currentTimeMillis(); if (lowTimestamp > 0l && lowTimestamp < (now - mcTime)) { // Major compaction time has elapsed. long cfTtl = this.storeConfigInfo.getStoreFileTtl(); if (filesToCompact.size() == 1) { // Single file StoreFile sf = filesToCompact.iterator().next(); Long minTimestamp = sf.getMinimumTimestamp(); long oldest = (minTimestamp == null) ? Long.MIN_VALUE : now - minTimestamp.longValue(); if (sf.isMajorCompaction() && (cfTtl == HConstants.FOREVER || oldest < cfTtl)) { if (LOG.isDebugEnabled()) { LOG.debug("Skipping major compaction of " + this + " because one (major) compacted file only and oldestTime " + oldest + "ms is < ttl=" + cfTtl); } } else if (cfTtl != HConstants.FOREVER && oldest > cfTtl) { LOG.debug("Major compaction triggered on store " + this + ", because keyvalues outdated; time since last major compaction " + (now - lowTimestamp) + "ms"); result = true; } } else { if (LOG.isDebugEnabled()) { LOG.debug("Major compaction triggered on store " + this + "; time since last major compaction " + (now - lowTimestamp) + "ms"); } result = true; } } return result; }
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