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Fix read capacity calculation and wait between scans #63

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Fix read capacity calculation and wait between scans #63

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69 changes: 45 additions & 24 deletions lib/dynamo-backup.js
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Original file line number Diff line number Diff line change
Expand Up @@ -159,38 +159,59 @@ DynamoBackup.prototype._copyTable = function (tableName, itemsReceived, callback
return callback(err);
}

var readPercentage = self.readPercentage;
var limit = Math.max((data.Table.ProvisionedThroughput.ReadCapacityUnits * readPercentage) | 0, 1);
const Table = data.Table;
var maxCapacityUnits = Math.max(Math.floor(Table.ProvisionedThroughput.ReadCapacityUnits * self.readPercentage), 1);
var averageItemSize = Table.TableSizeBytes / Table.ItemCount;

self._streamItems(tableName, null, limit, itemsReceived, callback);
self._streamItems(tableName, null, 0, maxCapacityUnits, averageItemSize, itemsReceived, callback);
});
};

DynamoBackup.prototype._streamItems = function fetchItems(tableName, startKey, limit, itemsReceived, callback) {
DynamoBackup.prototype._streamItems = function fetchItems(tableName, startKey, remainingCapacityUnits, maxCapacityUnits, averageItemSize, itemsReceived, callback) {
var self = this;
var ddb = new AWS.DynamoDB();
var params = {
Limit: limit,
ReturnConsumedCapacity: 'NONE',
TableName: tableName
};
if (startKey) {
params.ExclusiveStartKey = startKey;
}
ddb.scan(params, function (err, data) {
if (err) {
return callback(err);
}
var startOfSecond = new Date().getTime();

var usableCapacity = maxCapacityUnits + remainingCapacityUnits;
if (usableCapacity > 0) {
var limit = Math.max(Math.floor(((8 * 1024) / averageItemSize) * usableCapacity), 1);
var params = {
Limit: limit,
ReturnConsumedCapacity: 'TOTAL',
TableName: tableName
};

if (data.Items.length > 0) {
itemsReceived(data.Items);
if (startKey) {
params.ExclusiveStartKey = startKey;
}

if (!data.LastEvaluatedKey || _.keys(data.LastEvaluatedKey).length === 0) {
return callback();
}
self._streamItems(tableName, data.LastEvaluatedKey, limit, itemsReceived, callback);
});
ddb.scan(params, function (error, data) {
if (error) {
callback(error);
return;
}

if (data.Items.length > 0) {
itemsReceived(data.Items);
}

if (!data.LastEvaluatedKey || _.keys(data.LastEvaluatedKey).length === 0) {
callback();
return;
}

var nextRemainingCapacity = usableCapacity - data.ConsumedCapacity.CapacityUnits;
var timeout = Math.max(1000 - (new Date().getTime() - startOfSecond), 0);
setTimeout(function () {
self._streamItems(tableName, data.LastEvaluatedKey, nextRemainingCapacity, maxCapacityUnits, averageItemSize, itemsReceived, callback);
}, timeout);
});
} else {
// Wait until we have capacity again
setTimeout(() => {
self._streamItems(tableName, startKey, usableCapacity, maxCapacityUnits, averageItemSize, itemsReceived, callback);
}, 1000);
}
};

DynamoBackup.prototype._fetchTables = function (lastTable, tables, callback) {
Expand Down Expand Up @@ -259,4 +280,4 @@ DynamoBackup.prototype._getDataPipelineAttributeValueKey = function (type) {
}
};

module.exports = DynamoBackup;
module.exports = DynamoBackup;