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From Micah Kornfield <emkornfi...@gmail.com>
Subject Re: [java][apache-arrow] Having problem in appending record batches to same arrow file
Date Fri, 12 Feb 2021 04:16:30 GMT
There isn't functionality like this that exists for appending data to a
file.  You could potentially open a file, read the footer back track to the
footer location and start writing again.  This wouldn't be atomic but cold
work (likely some lower level API would need to be exposed).

The other option is to write out an ArrowStream (so no random access) and
then start appending new record batches at the end (I would need to check
but it is possible there isn't an option to write a new schema to the same
file).

TL;DR; This would potentially require some refactoring of APIs.  I'm not
sure it is a good idea, what is the motivating use-case?

Thanks,
Micah

On Wed, Feb 10, 2021 at 12:14 AM Priyanshu LNU <t-plnu@microsoft.com> wrote:

> Hi,
>
> I am using Apache arrow in Java. I want to append stream of record batches
> to an already existing file.
>
> That means, I have a fileOutputStream. Using ArrowStreamWriter, I wrote
> some batches to this fileOutputStream. Now I close the fileOutputStream and
> then again start this stream to append some batches to it.
>
> The issue is that metadata gets appended again, so the streamreader is not
> able to read all the batches. So how Can I append stream of recordBatches
> to an existing file correctly without repetition of metadata in between?
>
>
>
> Below is part of Java code I am currently using:
>
>
>
> *public* *void* setupWrite(String filename, *boolean* useCustom) *throws*
> Exception {
>
>         File arrowFile = *validateFile*(filename, *false*);
>
>         *this*.fileOutputStream = *new* FileOutputStream(arrowFile);
>
>         Schema schema = makeSchema();
>
>         *this*.root = VectorSchemaRoot.*create*(schema, *this*.ra);
>
>         DictionaryProvider.MapDictionaryProvider provider = *new*
> DictionaryProvider.MapDictionaryProvider();
>
>         *this*.arrowStreamWriter=*new* ArrowStreamWriter(root,provider
> ,Channels.*newChannel*(*this*.fileOutputStream));
>
>
>
>         // Just to show some stuff about the schema and layout
>
>         System.*out*.println("Schema/Layout: ");
>
>         *for* (Field field : root.getSchema().getFields()) {
>
>             FieldVector vector = root.getVector(field.getName());
>
>             showFieldLayout(field, vector);
>
>         }
>
>         System.*out*.println("Generated " + *this*.entries + " data
> entries , batch size " + batchSize + " usingCustomWriter: " + useCustom + "
> useNullValues " + *this*.useNullValues);
>
>
>
>      // writing logic starts here
>
> //      arrowFileWriter.start();
>
>       arrowStreamWriter.start();
>
>
>
>       *for*(*int* i = 0; i < *this*.entries;) {
>
>           *int* toProcessItems = Math.*min*(*this*.batchSize, *this*.
> entries - i);
>
>           // set the batch row count
>
>           root.setRowCount(toProcessItems);
>
>           *for* (Field field : root.getSchema().getFields()) {
>
>               FieldVector vector = root.getVector(field.getName());
>
>              // System.out.println(vector.getMinorType());
>
>               *switch* (vector.getMinorType()) {
>
>                   *case* *INT*:
>
>                       writeFieldInt(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *BIGINT*:
>
>                       writeFieldLong(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *FLOAT4*:
>
>                       writeFieldFloat4(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *VARCHAR*:
>
>                       writeFieldVarchar(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *DATEDAY*:
>
>                       writeFieldDate(vector, i, toProcessItems);
>
>                       *break*;
>
>                // case VARBINARY:
>
>                  //   writeFieldVarBinary(vector, i, toProcessItems);
>
>                    // break;
>
>                   *default*:
>
>                       *throw* *new* Exception(" Not supported yet type: "
> + vector.getMinorType());
>
>               }
>
>           }
>
> //          arrowFileWriter.writeBatch();
>
>           arrowStreamWriter.writeBatch();
>
>           i+=toProcessItems;
>
>       }
>
>       arrowStreamWriter.end();
>
>       arrowStreamWriter.close();
>
>       fileOutputStream.flush();
>
>       fileOutputStream.close();
>
>
>
>
>
>
>
>
>
>
>
>
>
>       *this*.fileOutputStream = *new* FileOutputStream(arrowFile,*true*);
>
>       *this*.arrowStreamWriter=*new* ArrowStreamWriter(root,provider,
> *this*.fileOutputStream.getChannel());
>
>       arrowStreamWriter.start();
>
>       *for*(*int* i = 0; i < *this*.entries;) {
>
>           *int* toProcessItems = Math.*min*(*this*.batchSize, *this*.
> entries - i);
>
>           // set the batch row count
>
>           root.setRowCount(toProcessItems);
>
>           *for* (Field field : root.getSchema().getFields()) {
>
>               FieldVector vector = root.getVector(field.getName());
>
>              // System.out.println(vector.getMinorType());
>
>               *switch* (vector.getMinorType()) {
>
>                   *case* *INT*:
>
>                       writeFieldInt(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *BIGINT*:
>
>                       writeFieldLong(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *FLOAT4*:
>
>                       writeFieldFloat4(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *VARCHAR*:
>
>                       writeFieldVarchar(vector, i, toProcessItems);
>
>                       *break*;
>
>                   *case* *DATEDAY*:
>
>                       writeFieldDate(vector, i, toProcessItems);
>
>                       *break*;
>
>                // case VARBINARY:
>
>                  //   writeFieldVarBinary(vector, i, toProcessItems);
>
>                    // break;
>
>                   *default*:
>
>                       *throw* *new* Exception(" Not supported yet type: "
> + vector.getMinorType());
>
>               }
>
>           arrowStreamWriter.writeBatch();
>
>           i+=toProcessItems;
>
>       }
>
>       arrowStreamWriter.end();
>
>       arrowStreamWriter.close();
>
>       fileOutputStream.flush();
>
>       fileOutputStream.close();
>
>  }
>
>
>
>
>
> Thanks,
>
> Priyanshu
>
>
>

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