Examples with Deferred com.stumbleupon.async.Deferred used on opensource projects

Example 26 with Deferred

use of com.stumbleupon.async.Deferred in project opentsdb by OpenTSDB.

the class TSMeta method syncToStorage.

/**
   * Attempts a CompareAndSet storage call, loading the object from storage, 
   * synchronizing changes, and attempting a put. Also verifies that associated 
   * UID name mappings exist before merging.
   * <b>Note:</b> If the local object didn't have any fields set by the caller
   * or there weren't any changes, then the data will not be written and an 
   * exception will be thrown.
   * <b>Note:</b> We do not store the UIDMeta information with TSMeta's since
   * users may change a single UIDMeta object and we don't want to update every
   * TSUID that includes that object with the new data. Instead, UIDMetas are
   * merged into the TSMeta on retrieval so we always have canonical data. This
   * also saves space in storage. 
   * @param tsdb The TSDB to use for storage access
   * @param overwrite When the RPC method is PUT, will overwrite all user
   * accessible fields
   * @return True if the storage call was successful, false if the object was
   * modified in storage during the CAS call. If false, retry the call. Other 
   * failures will result in an exception being thrown.
   * @throws HBaseException if there was an issue
   * @throws IllegalArgumentException if parsing failed
   * @throws NoSuchUniqueId If any of the UID name mappings do not exist
   * @throws IllegalStateException if the data hasn't changed. This is OK!
   * @throws JSONException if the object could not be serialized
   */
public Deferred<Boolean> syncToStorage(final TSDB tsdb, final boolean overwrite) {
    if (tsuid == null || tsuid.isEmpty()) {
        throw new IllegalArgumentException("Missing TSUID");
    }
    boolean has_changes = false;
    for (Map.Entry<String, Boolean> entry : changed.entrySet()) {
        if (entry.getValue()) {
            has_changes = true;
            break;
        }
    }
    if (!has_changes) {
        LOG.debug(this + " does not have changes, skipping sync to storage");
        throw new IllegalStateException("No changes detected in TSUID meta data");
    }
    /**
     * Callback used to verify that the UID name mappings exist. We don't need
     * to process the actual name, we just want it to throw an error if any
     * of the UIDs don't exist.
     */
    class UidCB implements Callback<Object, String> {

        @Override
        public Object call(String name) throws Exception {
            // nothing to do as missing mappings will throw a NoSuchUniqueId
            return null;
        }
    }
    // parse out the tags from the tsuid
    final List<byte[]> parsed_tags = UniqueId.getTagsFromTSUID(tsuid);
    // Deferred group used to accumulate UidCB callbacks so the next call
    // can wait until all of the UIDs have been verified
    ArrayList<Deferred<Object>> uid_group = new ArrayList<Deferred<Object>>(parsed_tags.size() + 1);
    // calculate the metric UID and fetch it's name mapping
    final byte[] metric_uid = UniqueId.stringToUid(tsuid.substring(0, TSDB.metrics_width() * 2));
    uid_group.add(tsdb.getUidName(UniqueIdType.METRIC, metric_uid).addCallback(new UidCB()));
    int idx = 0;
    for (byte[] tag : parsed_tags) {
        if (idx % 2 == 0) {
            uid_group.add(tsdb.getUidName(UniqueIdType.TAGK, tag).addCallback(new UidCB()));
        } else {
            uid_group.add(tsdb.getUidName(UniqueIdType.TAGV, tag).addCallback(new UidCB()));
        }
        idx++;
    }
    /**
     * Callback executed after all of the UID mappings have been verified. This
     * will then proceed with the CAS call.
     */
    final class ValidateCB implements Callback<Deferred<Boolean>, ArrayList<Object>> {

        private final TSMeta local_meta;

        public ValidateCB(final TSMeta local_meta) {
            this.local_meta = local_meta;
        }

        /**
       * Nested class that executes the CAS after retrieving existing TSMeta
       * from storage.
       */
        final class StoreCB implements Callback<Deferred<Boolean>, TSMeta> {

            /**
         * Executes the CAS if the TSMeta was successfully retrieved
         * @return True if the CAS was successful, false if the stored data
         * was modified in flight
         * @throws IllegalArgumentException if the TSMeta did not exist in
         * storage. Only the TSD should be able to create TSMeta objects.
         */
            @Override
            public Deferred<Boolean> call(TSMeta stored_meta) throws Exception {
                if (stored_meta == null) {
                    throw new IllegalArgumentException("Requested TSMeta did not exist");
                }
                final byte[] original_meta = stored_meta.getStorageJSON();
                local_meta.syncMeta(stored_meta, overwrite);
                final PutRequest put = new PutRequest(tsdb.metaTable(), UniqueId.stringToUid(local_meta.tsuid), FAMILY, META_QUALIFIER, local_meta.getStorageJSON());
                return tsdb.getClient().compareAndSet(put, original_meta);
            }
        }

        /**
       * Called on UID mapping verification and continues executing the CAS 
       * procedure.
       * @return Results from the {@link #StoreCB} callback
       */
        @Override
        public Deferred<Boolean> call(ArrayList<Object> validated) throws Exception {
            return getFromStorage(tsdb, UniqueId.stringToUid(tsuid)).addCallbackDeferring(new StoreCB());
        }
    }
    // Begins the callback chain by validating that the UID mappings exist
    return Deferred.group(uid_group).addCallbackDeferring(new ValidateCB(this));
}

Example 27 with Deferred

use of com.stumbleupon.async.Deferred in project opentsdb by OpenTSDB.

the class TSUIDQuery method getLastWriteTimes.

/**
   * Fetches a list of TSUIDs given the metric and optional tag pairs. The query
   * format is similar to TsdbQuery but doesn't support grouping operators for 
   * tags. Only TSUIDs that had "ts_counter" qualifiers will be returned.
   * <p>
   * NOTE: If you called {@link #setQuery(String, Map)} successfully this will
   * immediately scan the meta table. But if you used the CTOR to set the
   * metric and tags it will attempt to resolve those and may return an exception.
   * @return A map of TSUIDs to the last timestamp (in milliseconds) when the
   * "ts_counter" was updated. Note that the timestamp will be the time stored
   * by HBase, not the actual timestamp of the data point. If nothing was
   * found, the map will be empty but not null.
   * @throws IllegalArgumentException if the metric was not set or the tag map
   * was null
   */
public Deferred<ByteMap<Long>> getLastWriteTimes() {
    class ResolutionCB implements Callback<Deferred<ByteMap<Long>>, Object> {

        @Override
        public Deferred<ByteMap<Long>> call(Object arg0) throws Exception {
            final Scanner scanner = getScanner();
            scanner.setQualifier(TSMeta.COUNTER_QUALIFIER());
            final Deferred<ByteMap<Long>> results = new Deferred<ByteMap<Long>>();
            final ByteMap<Long> tsuids = new ByteMap<Long>();
            final class ErrBack implements Callback<Object, Exception> {

                @Override
                public Object call(final Exception e) throws Exception {
                    results.callback(e);
                    return null;
                }

                @Override
                public String toString() {
                    return "Error callback";
                }
            }
            /**
         * Scanner callback that will call itself while iterating through the 
         * tsdb-meta table
         */
            final class ScannerCB implements Callback<Object, ArrayList<ArrayList<KeyValue>>> {

                /**
           * Starts the scanner and is called recursively to fetch the next set of
           * rows from the scanner.
           * @return The map of spans if loaded successfully, null if no data was
           * found
           */
                public Object scan() {
                    return scanner.nextRows().addCallback(this).addErrback(new ErrBack());
                }

                /**
           * Loops through each row of the scanner results and parses out data
           * points and optional meta data
           * @return null if no rows were found, otherwise the TreeMap with spans
           */
                @Override
                public Object call(final ArrayList<ArrayList<KeyValue>> rows) throws Exception {
                    try {
                        if (rows == null) {
                            results.callback(tsuids);
                            return null;
                        }
                        for (final ArrayList<KeyValue> row : rows) {
                            final byte[] tsuid = row.get(0).key();
                            tsuids.put(tsuid, row.get(0).timestamp());
                        }
                        return scan();
                    } catch (Exception e) {
                        results.callback(e);
                        return null;
                    }
                }
            }
            new ScannerCB().scan();
            return results;
        }

        @Override
        public String toString() {
            return "Last counter time callback";
        }
    }
    if (metric_uid == null) {
        return resolveMetric().addCallbackDeferring(new ResolutionCB());
    }
    try {
        return new ResolutionCB().call(null);
    } catch (Exception e) {
        return Deferred.fromError(e);
    }
}

Example 28 with Deferred

use of com.stumbleupon.async.Deferred in project opentsdb by OpenTSDB.

the class HttpJsonSerializer method formatQueryAsyncV1.

/**
   * Format the results from a timeseries data query
   * @param data_query The TSQuery object used to fetch the results
   * @param results The data fetched from storage
   * @param globals An optional list of global annotation objects
   * @return A Deferred<ChannelBuffer> object to pass on to the caller
   * @throws IOException if serialization failed
   * @since 2.2
   */
public Deferred<ChannelBuffer> formatQueryAsyncV1(final TSQuery data_query, final List<DataPoints[]> results, final List<Annotation> globals) throws IOException {
    final long start = DateTime.currentTimeMillis();
    final boolean as_arrays = this.query.hasQueryStringParam("arrays");
    final String jsonp = this.query.getQueryStringParam("jsonp");
    // buffers and an array list to stored the deferreds
    final ChannelBuffer response = ChannelBuffers.dynamicBuffer();
    final OutputStream output = new ChannelBufferOutputStream(response);
    // too bad an inner class can't modify a primitive. This is a work around 
    final List<Boolean> timeout_flag = new ArrayList<Boolean>(1);
    timeout_flag.add(false);
    // start with JSONp if we're told to
    if (jsonp != null && !jsonp.isEmpty()) {
        output.write((jsonp + "(").getBytes(query.getCharset()));
    }
    // start the JSON generator and write the opening array
    final JsonGenerator json = JSON.getFactory().createGenerator(output);
    json.writeStartArray();
    /**
     * Every individual data point set (the result of a query and possibly a
     * group by) will initiate an asynchronous metric/tag UID to name resolution
     * and then print to the buffer.
     * NOTE that because this is asynchronous, the order of results is
     * indeterminate.
     */
    class DPsResolver implements Callback<Deferred<Object>, Object> {

        /** Has to be final to be shared with the nested classes */
        final StringBuilder metric = new StringBuilder(256);

        /** Resolved tags */
        final Map<String, String> tags = new HashMap<String, String>();

        /** Resolved aggregated tags */
        final List<String> agg_tags = new ArrayList<String>();

        /** A list storing the metric and tag resolve calls */
        final List<Deferred<Object>> resolve_deferreds = new ArrayList<Deferred<Object>>();

        /** The data points to serialize */
        final DataPoints dps;

        /** Starting time in nanos when we sent the UID resolution queries off */
        long uid_start;

        public DPsResolver(final DataPoints dps) {
            this.dps = dps;
        }

        /** Resolves the metric UID to a name*/
        class MetricResolver implements Callback<Object, String> {

            public Object call(final String metric) throws Exception {
                DPsResolver.this.metric.append(metric);
                return null;
            }
        }

        /** Resolves the tag UIDs to a key/value string set */
        class TagResolver implements Callback<Object, Map<String, String>> {

            public Object call(final Map<String, String> tags) throws Exception {
                DPsResolver.this.tags.putAll(tags);
                return null;
            }
        }

        /** Resolves aggregated tags */
        class AggTagResolver implements Callback<Object, List<String>> {

            public Object call(final List<String> tags) throws Exception {
                DPsResolver.this.agg_tags.addAll(tags);
                return null;
            }
        }

        /** After the metric and tags have been resolved, this will print the
       * results to the output buffer in the proper format.
       */
        class WriteToBuffer implements Callback<Object, ArrayList<Object>> {

            final DataPoints dps;

            /**
         * Default ctor that takes a data point set
         * @param dps Datapoints to print
         */
            public WriteToBuffer(final DataPoints dps) {
                this.dps = dps;
            }

            /**
         * Handles writing the data to the output buffer. The results of the
         * deferreds don't matter as they will be stored in the class final
         * variables.
         */
            public Object call(final ArrayList<Object> deferreds) throws Exception {
                data_query.getQueryStats().addStat(dps.getQueryIndex(), QueryStat.UID_TO_STRING_TIME, (DateTime.nanoTime() - uid_start));
                final long local_serialization_start = DateTime.nanoTime();
                final TSSubQuery orig_query = data_query.getQueries().get(dps.getQueryIndex());
                json.writeStartObject();
                json.writeStringField("metric", metric.toString());
                json.writeFieldName("tags");
                json.writeStartObject();
                if (dps.getTags() != null) {
                    for (Map.Entry<String, String> tag : tags.entrySet()) {
                        json.writeStringField(tag.getKey(), tag.getValue());
                    }
                }
                json.writeEndObject();
                json.writeFieldName("aggregateTags");
                json.writeStartArray();
                if (dps.getAggregatedTags() != null) {
                    for (String atag : agg_tags) {
                        json.writeString(atag);
                    }
                }
                json.writeEndArray();
                if (data_query.getShowQuery()) {
                    json.writeObjectField("query", orig_query);
                }
                if (data_query.getShowTSUIDs()) {
                    json.writeFieldName("tsuids");
                    json.writeStartArray();
                    final List<String> tsuids = dps.getTSUIDs();
                    Collections.sort(tsuids);
                    for (String tsuid : tsuids) {
                        json.writeString(tsuid);
                    }
                    json.writeEndArray();
                }
                if (!data_query.getNoAnnotations()) {
                    final List<Annotation> annotations = dps.getAnnotations();
                    if (annotations != null) {
                        Collections.sort(annotations);
                        json.writeArrayFieldStart("annotations");
                        for (Annotation note : annotations) {
                            json.writeObject(note);
                        }
                        json.writeEndArray();
                    }
                    if (globals != null && !globals.isEmpty()) {
                        Collections.sort(globals);
                        json.writeArrayFieldStart("globalAnnotations");
                        for (Annotation note : globals) {
                            json.writeObject(note);
                        }
                        json.writeEndArray();
                    }
                }
                // now the fun stuff, dump the data and time just the iteration over
                // the data points
                final long dps_start = DateTime.nanoTime();
                json.writeFieldName("dps");
                long counter = 0;
                // default is to write a map, otherwise write arrays
                if (!timeout_flag.get(0) && as_arrays) {
                    json.writeStartArray();
                    for (final DataPoint dp : dps) {
                        if (dp.timestamp() < data_query.startTime() || dp.timestamp() > data_query.endTime()) {
                            continue;
                        }
                        final long timestamp = data_query.getMsResolution() ? dp.timestamp() : dp.timestamp() / 1000;
                        json.writeStartArray();
                        json.writeNumber(timestamp);
                        if (dp.isInteger()) {
                            json.writeNumber(dp.longValue());
                        } else {
                            // Report missing intervals as null or NaN.
                            final double value = dp.doubleValue();
                            if (Double.isNaN(value) && orig_query.fillPolicy() == FillPolicy.NULL) {
                                json.writeNull();
                            } else {
                                json.writeNumber(dp.doubleValue());
                            }
                        }
                        json.writeEndArray();
                        ++counter;
                    }
                    json.writeEndArray();
                } else if (!timeout_flag.get(0)) {
                    json.writeStartObject();
                    for (final DataPoint dp : dps) {
                        if (dp.timestamp() < (data_query.startTime()) || dp.timestamp() > (data_query.endTime())) {
                            continue;
                        }
                        final long timestamp = data_query.getMsResolution() ? dp.timestamp() : dp.timestamp() / 1000;
                        if (dp.isInteger()) {
                            json.writeNumberField(Long.toString(timestamp), dp.longValue());
                        } else {
                            // Report missing intervals as null or NaN.
                            final double value = dp.doubleValue();
                            if (Double.isNaN(value) && orig_query.fillPolicy() == FillPolicy.NULL) {
                                json.writeNumberField(Long.toString(timestamp), null);
                            } else {
                                json.writeNumberField(Long.toString(timestamp), dp.doubleValue());
                            }
                        }
                        ++counter;
                    }
                    json.writeEndObject();
                } else {
                    // skipping data points all together due to timeout
                    json.writeStartObject();
                    json.writeEndObject();
                }
                final long agg_time = DateTime.nanoTime() - dps_start;
                data_query.getQueryStats().addStat(dps.getQueryIndex(), QueryStat.AGGREGATION_TIME, agg_time);
                data_query.getQueryStats().addStat(dps.getQueryIndex(), QueryStat.AGGREGATED_SIZE, counter);
                // yeah, it's a little early but we need to dump it out with the results.
                data_query.getQueryStats().addStat(dps.getQueryIndex(), QueryStat.SERIALIZATION_TIME, DateTime.nanoTime() - local_serialization_start);
                if (!timeout_flag.get(0) && data_query.getShowStats()) {
                    int query_index = (dps == null) ? -1 : dps.getQueryIndex();
                    QueryStats stats = data_query.getQueryStats();
                    if (query_index >= 0) {
                        json.writeFieldName("stats");
                        final Map<String, Object> s = stats.getQueryStats(query_index, false);
                        if (s != null) {
                            json.writeObject(s);
                        } else {
                            json.writeStringField("ERROR", "NO STATS FOUND");
                        }
                    }
                }
                // close the results for this particular query
                json.writeEndObject();
                return null;
            }
        }

        /**
       * When called, initiates a resolution of metric and tag UIDs to names, 
       * then prints to the output buffer once they are completed.
       */
        public Deferred<Object> call(final Object obj) throws Exception {
            this.uid_start = DateTime.nanoTime();
            resolve_deferreds.add(dps.metricNameAsync().addCallback(new MetricResolver()));
            resolve_deferreds.add(dps.getTagsAsync().addCallback(new TagResolver()));
            resolve_deferreds.add(dps.getAggregatedTagsAsync().addCallback(new AggTagResolver()));
            return Deferred.group(resolve_deferreds).addCallback(new WriteToBuffer(dps));
        }
    }
    // We want the serializer to execute serially so we need to create a callback
    // chain so that when one DPsResolver is finished, it triggers the next to
    // start serializing.
    final Deferred<Object> cb_chain = new Deferred<Object>();
    for (DataPoints[] separate_dps : results) {
        for (DataPoints dps : separate_dps) {
            try {
                cb_chain.addCallback(new DPsResolver(dps));
            } catch (Exception e) {
                throw new RuntimeException("Unexpected error durring resolution", e);
            }
        }
    }
    /** Final callback to close out the JSON array and return our results */
    class FinalCB implements Callback<ChannelBuffer, Object> {

        public ChannelBuffer call(final Object obj) throws Exception {
            // Call this here so we rollup sub metrics into a summary. It's not
            // completely accurate, of course, because we still have to write the
            // summary and close the writer. But it's close.
            data_query.getQueryStats().markSerializationSuccessful();
            // TODO - yeah, I've heard this sucks, we need to figure out a better way.
            if (data_query.getShowSummary()) {
                final QueryStats stats = data_query.getQueryStats();
                json.writeStartObject();
                json.writeFieldName("statsSummary");
                json.writeObject(stats.getStats(true, true));
                json.writeEndObject();
            }
            // IMPORTANT Make sure the close the JSON array and the generator
            json.writeEndArray();
            json.close();
            if (jsonp != null && !jsonp.isEmpty()) {
                output.write(")".getBytes());
            }
            return response;
        }
    }
    // trigger the callback chain here
    cb_chain.callback(null);
    return cb_chain.addCallback(new FinalCB());
}

Example 29 with Deferred

use of com.stumbleupon.async.Deferred in project opentsdb by OpenTSDB.

the class AnnotationRpc method execute.

/**
   * Performs CRUD methods on individual annotation objects.
   * @param tsdb The TSD to which we belong
   * @param query The query to parse and respond to
   */
public void execute(final TSDB tsdb, HttpQuery query) throws IOException {
    final HttpMethod method = query.getAPIMethod();
    final String[] uri = query.explodeAPIPath();
    final String endpoint = uri.length > 1 ? uri[1] : "";
    if (endpoint != null && endpoint.toLowerCase().endsWith("bulk")) {
        executeBulk(tsdb, method, query);
        return;
    }
    final Annotation note;
    if (query.hasContent()) {
        note = query.serializer().parseAnnotationV1();
    } else {
        note = parseQS(query);
    }
    // GET
    if (method == HttpMethod.GET) {
        try {
            if ("annotations".toLowerCase().equals(uri[0])) {
                fetchMultipleAnnotations(tsdb, note, query);
            } else {
                fetchSingleAnnotation(tsdb, note, query);
            }
        } catch (BadRequestException e) {
            throw e;
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    // POST
    } else if (method == HttpMethod.POST || method == HttpMethod.PUT) {
        /**
       * Storage callback used to determine if the storage call was successful
       * or not. Also returns the updated object from storage.
       */
        class SyncCB implements Callback<Deferred<Annotation>, Boolean> {

            @Override
            public Deferred<Annotation> call(Boolean success) throws Exception {
                if (!success) {
                    throw new BadRequestException(HttpResponseStatus.INTERNAL_SERVER_ERROR, "Failed to save the Annotation to storage", "This may be caused by another process modifying storage data");
                }
                return Annotation.getAnnotation(tsdb, note.getTSUID(), note.getStartTime());
            }
        }
        try {
            final Deferred<Annotation> process_meta = note.syncToStorage(tsdb, method == HttpMethod.PUT).addCallbackDeferring(new SyncCB());
            final Annotation updated_meta = process_meta.joinUninterruptibly();
            tsdb.indexAnnotation(note);
            query.sendReply(query.serializer().formatAnnotationV1(updated_meta));
        } catch (IllegalStateException e) {
            query.sendStatusOnly(HttpResponseStatus.NOT_MODIFIED);
        } catch (IllegalArgumentException e) {
            throw new BadRequestException(e);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    // DELETE    
    } else if (method == HttpMethod.DELETE) {
        try {
            note.delete(tsdb).joinUninterruptibly();
            tsdb.deleteAnnotation(note);
        } catch (IllegalArgumentException e) {
            throw new BadRequestException("Unable to delete Annotation information", e);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
        query.sendStatusOnly(HttpResponseStatus.NO_CONTENT);
    } else {
        throw new BadRequestException(HttpResponseStatus.METHOD_NOT_ALLOWED, "Method not allowed", "The HTTP method [" + method.getName() + "] is not permitted for this endpoint");
    }
}

Example 30 with Deferred

use of com.stumbleupon.async.Deferred in project opentsdb by OpenTSDB.

the class MetaPurge method purgeUIDMeta.

/**
   * Scans the entire UID table and removes any UIDMeta objects found.
   * @return The total number of columns deleted
   */
public Deferred<Long> purgeUIDMeta() {
    // a list to store all pending deletes so we don't exit before they've 
    // completed
    final ArrayList<Deferred<Object>> delete_calls = new ArrayList<Deferred<Object>>();
    final Deferred<Long> result = new Deferred<Long>();
    /**
     * Scanner callback that will recursively call itself and loop through the
     * rows of the UID table, issuing delete requests for all of the columns in
     * a row that match a meta qualifier.
     */
    final class MetaScanner implements Callback<Deferred<Long>, ArrayList<ArrayList<KeyValue>>> {

        final Scanner scanner;

        public MetaScanner() {
            scanner = getScanner(tsdb.uidTable());
        }

        /**
       * Fetches the next group of rows from the scanner and sets this class as
       * a callback
       * @return The total number of columns deleted after completion
       */
        public Deferred<Long> scan() {
            return scanner.nextRows().addCallbackDeferring(this);
        }

        @Override
        public Deferred<Long> call(ArrayList<ArrayList<KeyValue>> rows) throws Exception {
            if (rows == null) {
                result.callback(columns);
                return null;
            }
            for (final ArrayList<KeyValue> row : rows) {
                // one delete request per row. We'll almost always delete the whole
                // row, so preallocate some ram.
                ArrayList<byte[]> qualifiers = new ArrayList<byte[]>(row.size());
                for (KeyValue column : row) {
                    if (Bytes.equals(TSMeta.META_QUALIFIER(), column.qualifier())) {
                        qualifiers.add(column.qualifier());
                    } else if (Bytes.equals("metric_meta".getBytes(CHARSET), column.qualifier())) {
                        qualifiers.add(column.qualifier());
                    } else if (Bytes.equals("tagk_meta".getBytes(CHARSET), column.qualifier())) {
                        qualifiers.add(column.qualifier());
                    } else if (Bytes.equals("tagv_meta".getBytes(CHARSET), column.qualifier())) {
                        qualifiers.add(column.qualifier());
                    }
                }
                if (qualifiers.size() > 0) {
                    columns += qualifiers.size();
                    final DeleteRequest delete = new DeleteRequest(tsdb.uidTable(), row.get(0).key(), NAME_FAMILY, qualifiers.toArray(new byte[qualifiers.size()][]));
                    delete_calls.add(tsdb.getClient().delete(delete));
                }
            }
            /**
         * Buffer callback used to wait on all of the delete calls for the
         * last set of rows returned from the scanner so we don't fill up the
         * deferreds array and OOM out.
         */
            final class ContinueCB implements Callback<Deferred<Long>, ArrayList<Object>> {

                @Override
                public Deferred<Long> call(ArrayList<Object> deletes) throws Exception {
                    LOG.debug("[" + thread_id + "] Processed [" + deletes.size() + "] delete calls");
                    delete_calls.clear();
                    return scan();
                }
            }
            // fetch the next set of rows after waiting for current set of delete
            // requests to complete
            Deferred.group(delete_calls).addCallbackDeferring(new ContinueCB());
            return null;
        }
    }
    // start the scan
    new MetaScanner().scan();
    return result;
}