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https://issues.apache.org/jira/browse/ACCUMULO-3913?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eric Newton updated ACCUMULO-3913:
----------------------------------
Description:
I am working on prototyping adding hash based sampling to Accumulo. I am
trying to accomplish the following goals in the prototype.
# Have each RFile store a sample per locality group. Also store the
configuration used to generate the sample.
# Use sampling functions that ensure the same row columns exist across the
samples in all RFiles. Hash mod is a good candidate that gives a random sample
that's consistent across files.
# Have scanners support scanning RFile's samples sets. Scan should fail if
RFiles have different sample configuration. Different sampling config implies
the RFile's sample sets contain a possibly disjoint set of row columns.
# Support generating sample data for RFiles generated for bulk import
# Support sample data in the memory map
# Support enabling and disabling sampling per table AND configuring a sample
function.
I am currently using the following function in my prototype to determine what
data an RFile stores in its sample set. This code will always select same
subset of rows for each RFile's sample set. I have not yet made the function
configurable.
{code:java}
public class RowSampler implements Sampler {
private HashFunction hasher = Hashing.murmur3_32();
@Override
public boolean accept(Key k) {
ByteSequence row = k.getRowData();
HashCode hc = hasher.hashBytes(row.getBackingArray(), row.offset(),
row.length());
return hc.asInt() % 1009 == 0;
}
}
{code}
Although not yet implemented, the divisor in this RowSample could be
configurable. RFiles with sample data would store the fact that a RowSample
with a divisor of 1009 was used to generate sample data.
was:
I am working on prototyping adding hash based sampling to Accumulo. I am
trying to accomplish the following goals in the prototype.
# Have each RFile store a sample per locality group. Also store the
configuration used to generate the sample.
# Use sampling functions that ensure the same row columns exist across the
samples in all rfiles. Hash mod is a good candidate that gives a random sample
thats consistent across files.
# Have scanners support scanning RFile's samples sets. Scan should fail if
RFiles have different sample configuration. Different sampling config implies
the RFile's sample sets contain a possibly disjoint set of row columns.
# Support generating sample data for RFiles generated for bulk import
# Support sample data in in memory map
# Support enabling and disabling sampling per table AND configuring a sample
function.
I am currently using the following function in my prototype to determine what
data an RFile stores in its sample set. This code will always select same
subset of rows for each RFile's sample set. I have not yet made the function
configurable.
{code:java}
public class RowSampler implements Sampler {
private HashFunction hasher = Hashing.murmur3_32();
@Override
public boolean accept(Key k) {
ByteSequence row = k.getRowData();
HashCode hc = hasher.hashBytes(row.getBackingArray(), row.offset(),
row.length());
return hc.asInt() % 1009 == 0;
}
}
{code}
Although not yet implemented, the divisor in this RowSample could be
configurable. RFiles with sample data would store the fact that a RowSample
with a divisor of 1009 was used to generate sample data.
> Add per table sampling
> ----------------------
>
> Key: ACCUMULO-3913
> URL: https://issues.apache.org/jira/browse/ACCUMULO-3913
> Project: Accumulo
> Issue Type: Bug
> Reporter: Keith Turner
> Fix For: 1.8.0
>
>
> I am working on prototyping adding hash based sampling to Accumulo. I am
> trying to accomplish the following goals in the prototype.
> # Have each RFile store a sample per locality group. Also store the
> configuration used to generate the sample.
> # Use sampling functions that ensure the same row columns exist across the
> samples in all RFiles. Hash mod is a good candidate that gives a random
> sample that's consistent across files.
> # Have scanners support scanning RFile's samples sets. Scan should fail if
> RFiles have different sample configuration. Different sampling config
> implies the RFile's sample sets contain a possibly disjoint set of row
> columns.
> # Support generating sample data for RFiles generated for bulk import
> # Support sample data in the memory map
> # Support enabling and disabling sampling per table AND configuring a
> sample function.
> I am currently using the following function in my prototype to determine what
> data an RFile stores in its sample set. This code will always select same
> subset of rows for each RFile's sample set. I have not yet made the function
> configurable.
> {code:java}
> public class RowSampler implements Sampler {
> private HashFunction hasher = Hashing.murmur3_32();
> @Override
> public boolean accept(Key k) {
> ByteSequence row = k.getRowData();
> HashCode hc = hasher.hashBytes(row.getBackingArray(), row.offset(),
> row.length());
> return hc.asInt() % 1009 == 0;
> }
> }
> {code}
> Although not yet implemented, the divisor in this RowSample could be
> configurable. RFiles with sample data would store the fact that a RowSample
> with a divisor of 1009 was used to generate sample data.
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