Nifi merge content
The MergeContent processor in Apache NiFi is one of the most useful processors but can also be one of the biggest sources of confusion. The processor you guessed it! In this post we describe how it can be used to merge this site was designed using vi, and is very plain because i don split flowfiles together.
In a recent NiFi flow, the flow was being split into separate pipelines. Both pipelines executed independently and when both were complete they were merged back into a single flowfile.REST API concepts and examples
In MergeContent-speak, the split flowfiles became fragments. There are two fragments and we can refer to them as 0 and 1. What does matter is that the index is unique and less than the fragment count 2. Using the Defragment merge strategy requires some attributes to be placed on the flowfile.
Those attributes are:. You can set these attributes using an UpdateAttribute processor. In the screenshot below, our flowfile was previously split into 5 fragments. The common attribute value across each of the fragments is some. This UpdateAttribute processor is setting this flowfile as index 0. With these attributes set, when flowfiles reach the MergeContent processor it will know how to combine them.
As flowfiles come into the MergeContent processor the value of the fragment. The MergeContent will bin the flowfiles based on this attribute. When the count of flowfiles binned equals the fragment.
So, if your flow has flowfiles with unique fragment. The other properties of the MergeContent processor are mostly self-explanatory. For example, if you are merging text you can set the Demarcator property to separate the text. The Header and Footer properties allow you to sandwich the combined text with some values. The same flowfile fragments are both at position N. This means that one part of the flowfile is on one node and the other part is on the other node, hence the stuck flowfiles.
You need to ensure that the upstream flow is putting the flowfiles onto the same NiFi node. This will ensure that flowfiles with the same value for the some. For more on load balancing check out this blog post from the Apache NiFi project. My Account. In blog.
By mtnfog. Related Posts Philter Studio 1.The MergeRecord Processor allows the user to take many FlowFiles that consist of record-oriented data any data format for which there is a Record Reader available and combine the FlowFiles into one larger FlowFile. This may be preferable before pushing the data to a downstream system that prefers larger batches of data, such as HDFS, or in order to improve performance of a NiFi flow by reducing the number of FlowFiles that flow through the system thereby reducing the contention placed on the FlowFile Repository, Provenance Repository, Content Repository, and FlowFile Queues.
The Processor creates several 'bins' to put the FlowFiles in. The number of bins is bound in order to avoid running out of Java heap space. Note: while the contents of a FlowFile are stored in the Content Repository and not in the Java heap space, the Processor must hold the FlowFile objects themselves in memory.
As a result, these FlowFiles with their attributes can potentially take up a great deal of heap space and cause OutOfMemoryError's to be thrown.
In order to avoid this, if you expect to merge many small FlowFiles together, it is advisable to instead use a MergeContent that merges no more than say 1, FlowFiles into a bundle and then use a second MergeContent to merges these small bundles into larger bundles.
The second MergeRecord will then merge 1, bundles of 1, which in effect produces bundles of 1, How the Processor determines which bin to place a FlowFile in depends on a few different configuration options. Firstly, the Merge Strategy is considered. What it means for two FlowFiles to be 'like FlowFiles' is discussed at the end of this section. The "Defragment" Merge Strategy can be used when records need to be explicitly assigned to the same bin.
For example, if data is split apart using the SplitRecord Processor, each 'split' can be processed independently and later merged back together using this Processor with the Merge Strategy set to Defragment. In order for FlowFiles to be added to the same bin when using this configuration, the FlowFiles must have the same value for the "fragment. Each FlowFile with the same identifier must also have the same value for the "fragment. In order to be added to the same bin, two FlowFiles must be 'like FlowFiles.
If more than one attribute is needed in order to correlate two FlowFiles, it is recommended to use an UpdateAttribute processor before the MergeRecord processor and combine the attributes. For example, if the goal is to bin together two FlowFiles only if they have the same value for the "abc" attribute and the "xyz" attribute, then we could accomplish this by using UpdateAttribute and adding a property with name "correlation.
It is often useful to bin together only Records that have the same value for some field. For example, if we have point-of-sale data, perhaps the desire is to bin together records that belong to the same store, as identified by the 'storeId' field. This Processor will allow one or more fields to be configured as the partitioning criteria and will create attributes for those corresponding values. An UpdateAttribute processor could then be used, if necessary, to combine multiple attributes into a single correlation attribute, as described above.
See documentation for those processors for more details. Above, we discussed how a bin is chosen for a given FlowFile. Once a bin has been created and FlowFiles added to it, we must have some way to determine when a bin is "full" so that we can bin those FlowFiles together into a "merged" FlowFile.
There are a few criteria that are used to make a determination as to whether or not a bin should be merged. If one of these properties is not set, then it is ignored. That is, both of the minimum values must be reached but only one of the maximum values need be reached. Once this happens, though, no more Records will be added to that same bin from another FlowFile.
This is done because otherwise we would not be able to add any additional FlowFiles to the existing bins and would have to wait until the Max Bin Age is reached if ever in order to merge any FlowFiles.SplitText back to a single flow file.
However, sometimes things can be more complicated than that. This post describes the recent improvement that I worked on, to wait for all fragments to be processed. I designed NiFi flow as follows. There are 4 areas in this flow and it looks like a traditional nested for loop using i and j:. I split into 5, lines chunks here.
Apache NiFi’s MergeContent Processor
Then connect the original relationship into a Wait processor. Here is a list of important Wait processor configurations:. When Wait processor finds chunks counter reached to fragment. Each chunk is passed into another SplitText here, then it produces flow file per individual record.
Similar to the previous part, connect original to a Wait processor, which is configured as follows:.
When Wait finds all Records in a Chunk has notified, it passes the flow file to Notify which notifies to the corresponding Wait processor in the previous part. In this area, you can do whatever record level processing, such as filter, convert, enrich or call APIs … etc.
To make it as simple as possible, I just route records into two groups, kept and filteredby RouteOnAttribute:. The next processor in both routes is UpdateAttribute, which adds counter. The first green one is used for adding Record process result counter into the signal that the root Wait processor is waiting for, so that downstream processing can use those counts.
The final Notify processor notifies that records are processed, and configured like below:. If everything is set up correctly, when files are passed to the input port, it will be split into chunks first, then records, and all records and chunks are processed, the original input file is routed to the output port. As another benefit of this approach, the outgoing flow file has following attributes added result of a file with 1M lines :. It works as expected in terms of functionality, but how about performance?
So, conducted following test. Of course it taks longer to complete, waiting asynchronous operations tends to be like that. However, by sacrificing performance a bit, you can design a NiFi flow that tracks record level processing result status, and keep processing order more strictly. Template file is available on Gist. How to wait for all fragments to be processed, then do something? This happens if some of the fragments have been filtered out.
First, split a file into mid-sized chunks, then split a chunk into individual record. This way, we can prevent NiFi to produce a lerge amount of flow file which can cause OutOfMemory error. We can copy those to avoid being overwritten, but flow looks messy if we actually do that. Split a file into Chunks I split into 5, lines chunks here. Split a Chunk into Records Each chunk is passed into another SplitText here, then it produces flow file per individual record.
Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I want to use MergeContent processor to merge tweets to bulk insert into Elasticsearch index. This is how it should look like. Is it possible to make it actual new line? Also is it possible to leave or make footer empty?
You are correct in that it takes the literal representation of what is entered. There are two ways to handle this:. With regards to your question on leaving the footer empty, it should work as you anticipate for the Merge Format of 'Binary Concatenation. Learn more. Asked 4 years, 3 months ago. Active 2 years, 5 months ago.
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Active Oldest Votes. NiFi 0. Dec 14 '15 at Thanks Apiri. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Skip to content.
Permalink Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. Branch: master. Find file Copy path. Cannot retrieve contributors at this time. Raw Blame History. BufferedInputStream ; import java. BufferedOutputStream ; import java. IOException ; import java. InputStream ; import java. OutputStream ; import java.
StandardCharsets ; import java. Files ; import java. Path ; import java. Paths ; import java. Instant ; import java. ArrayList ; import java. Arrays ; import java. Collection ; import java.If by merging you means doing an union, you can use the processor mergecontent if the two csv have the same structure. Best regards, Michel. Thanks for your answer. I tried to do that but it was creating files again and again and data was getting duplicated. I am having different metadata in all the files except one common column.
So which property i should use for Metadata Strategy in merge content processor. Based on your example, you are trying to do a "join". Nifi is not an ETL tool but more a flow manager, it allow to move data accros system and to do some very simple transformation like csv to avro.
You should not do computation or join with Nifi. For you usecase it would be better to use another tools like hive, spark, For your case you can use LookUpRecord processor to look for deptid and add get the salary,email and add to the record. Load your inputfile2 in one of the lookup services then use LookupRecord to look for deptid value then add the value to the record.
Refer to this and this links to get more details regarding configuration and working with LookupRecord processor. So it will merge all the records.
Shall i use the queryrecord processor befire or after the mergecontent.? This query Would be intensive if you are doing on larger number of records. Support Questions. Find answers, ask questions, and share your expertise. Turn on suggestions. Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.
Showing results for. Search instead for. Did you mean:. Cloudera Community : Support : Support Questions : merge too csv files in nifi. Alert: Welcome to the Unified Cloudera Community. Former HCC members be sure to read and learn how to activate your account here.Merges a Group of FlowFiles together based on a user-defined strategy and packages them into a single FlowFile.
It is recommended that the Processor be configured with only a single incoming connection, as Group of FlowFiles will not be created from FlowFiles in different connections.
This processor updates the mime. In the list below, the names of required properties appear in bold. Any other properties not in bold are considered optional. The table also indicates any default values, and whether a property supports the NiFi Expression Language. SegmentContentMergeRecord. Bin-Packing Algorithm Defragment. Specifies the algorithm used to merge content.
The 'Defragment' algorithm combines fragments that are associated by attributes back into a single cohesive FlowFile. Determines which FlowFile attributes should be added to the bundle. If 'Keep All Unique Attributes' is selected, any attribute on any FlowFile that gets bundled will be kept unless its value conflicts with the value from another FlowFile.
If 'Keep Only Common Attributes' is selected, only the attributes that exist on all FlowFiles in the bundle, with the same value, will be preserved.
If specified, like FlowFiles will be binned together, where 'like FlowFiles' means FlowFiles that have the same value for this Attribute. If not specified, FlowFiles are bundled by the order in which they are pulled from the queue. Supports Expression Language: true. For FlowFiles whose input format supports metadata Avro, e. If 'Keep Only Common Metadata' is selected, only the metadata that exists on all FlowFiles in the bundle, with the same value, will be preserved.
If 'Ignore Metadata' is selected, no metadata is transferred to the outgoing bundled FlowFile. The maximum number of files to include in a bundle. If not specified, there is no maximum. The maximum age of a Bin that will trigger a Bin to be complete. Specifies the maximum number of bins that can be held in memory at any one time.
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