cassandra-server
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A thin Javascript wrapper around Apache Cassandra to provide out of the box server support
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<h2 title="Class Downsampling" class="title">Class Downsampling</h2>
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<pre>public class <span class="strong">Downsampling</span>
extends java.lang.Object</pre>
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<td class="colFirst"><code>static int</code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/cassandra/io/sstable/Downsampling.html#BASE_SAMPLING_LEVEL">BASE_SAMPLING_LEVEL</a></strong></code>
<div class="block">The base (down)sampling level determines the granularity at which we can down/upsample.</div>
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<td class="colOne"><code><strong><a href="../../../../../org/apache/cassandra/io/sstable/Downsampling.html#Downsampling()">Downsampling</a></strong>()</code> </td>
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<td class="colFirst"><code>static int</code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/cassandra/io/sstable/Downsampling.html#getEffectiveIndexIntervalAfterIndex(int,%20int,%20int)">getEffectiveIndexIntervalAfterIndex</a></strong>(int index,
int samplingLevel,
int minIndexInterval)</code>
<div class="block">Calculates the effective index interval after the entry at `index` in an IndexSummary.</div>
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<td class="colFirst"><code>static java.util.List<java.lang.Integer></code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/cassandra/io/sstable/Downsampling.html#getOriginalIndexes(int)">getOriginalIndexes</a></strong>(int samplingLevel)</code>
<div class="block">Returns a list that can be used to translate current index summary indexes to their original index before
downsampling.</div>
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<td class="colFirst"><code>static java.util.List<java.lang.Integer></code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/cassandra/io/sstable/Downsampling.html#getSamplingPattern(int)">getSamplingPattern</a></strong>(int samplingLevel)</code>
<div class="block">Gets a list L of starting indices for downsampling rounds: the first round should start with the offset
given by L[0], the second by the offset in L[1], etc.</div>
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<td class="colFirst"><code>static int[]</code></td>
<td class="colLast"><code><strong><a href="../../../../../org/apache/cassandra/io/sstable/Downsampling.html#getStartPoints(int,%20int)">getStartPoints</a></strong>(int currentSamplingLevel,
int newSamplingLevel)</code> </td>
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<h4>BASE_SAMPLING_LEVEL</h4>
<pre>public static final int BASE_SAMPLING_LEVEL</pre>
<div class="block">The base (down)sampling level determines the granularity at which we can down/upsample.
A higher number allows us to approximate more closely the ideal sampling. (It could also mean we do a lot of
expensive almost-no-op resamplings from N to N-1, but the thresholds in IndexSummaryManager prevent that.)
BSL must be a power of two in order to have good sampling patterns. This cannot be changed without rebuilding
all index summaries at full sampling; for now we treat it as a constant.</div>
<dl><dt><span class="strong">See Also:</span></dt><dd><a href="../../../../../constant-values.html#org.apache.cassandra.io.sstable.Downsampling.BASE_SAMPLING_LEVEL">Constant Field Values</a></dd></dl>
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<h4>Downsampling</h4>
<pre>public Downsampling()</pre>
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<h4>getSamplingPattern</h4>
<pre>public static java.util.List<java.lang.Integer> getSamplingPattern(int samplingLevel)</pre>
<div class="block">Gets a list L of starting indices for downsampling rounds: the first round should start with the offset
given by L[0], the second by the offset in L[1], etc.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>samplingLevel</code> - the base sampling level</dd>
<dt><span class="strong">Returns:</span></dt><dd>A list of `samplingLevel` unique indices between 0 and `samplingLevel`</dd></dl>
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<h4>getOriginalIndexes</h4>
<pre>public static java.util.List<java.lang.Integer> getOriginalIndexes(int samplingLevel)</pre>
<div class="block">Returns a list that can be used to translate current index summary indexes to their original index before
downsampling. (This repeats every `samplingLevel`, so that's how many entries we return.)
For example, if [7, 15] is returned, the current index summary entry at index 0 was originally
at index 7, and the current index 1 was originally at index 15.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>samplingLevel</code> - the current sampling level for the index summary</dd>
<dt><span class="strong">Returns:</span></dt><dd>a list of original indexes for current summary entries</dd></dl>
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<h4>getEffectiveIndexIntervalAfterIndex</h4>
<pre>public static int getEffectiveIndexIntervalAfterIndex(int index,
int samplingLevel,
int minIndexInterval)</pre>
<div class="block">Calculates the effective index interval after the entry at `index` in an IndexSummary. In other words, this
returns the number of partitions in the primary on-disk index before the next partition that has an entry in
the index summary. If samplingLevel == BASE_SAMPLING_LEVEL, this will be equal to the index interval.</div>
<dl><dt><span class="strong">Parameters:</span></dt><dd><code>index</code> - an index into an IndexSummary</dd><dd><code>samplingLevel</code> - the current sampling level for that IndexSummary</dd><dd><code>minIndexInterval</code> - the min index interval (effective index interval at full sampling)</dd>
<dt><span class="strong">Returns:</span></dt><dd>the number of partitions before the next index summary entry, inclusive on one end</dd></dl>
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<pre>public static int[] getStartPoints(int currentSamplingLevel,
int newSamplingLevel)</pre>
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