Cheng Lian created SPARK-14274: ---------------------------------- Summary: Replaces inferSchema with prepareRead to collect necessary global information Key: SPARK-14274 URL: https://issues.apache.org/jira/browse/SPARK-14274 Project: Spark Issue Type: Sub-task Components: SQL Affects Versions: 2.0.0 Reporter: Cheng Lian Assignee: Cheng Lian
One problem of our newly introduced {{FileFormat.buildReader()}} method is that it only sees pieces of input files. On the other hand, data sources like CSV and LibSVM requires some sort of global information: - CSV: the content of the header line if {{header}} option is set to true, so that we can filter out header lines within each input file. This is considered as a global information because it's possible that the header appears in the middle of a file after blocks of comments and empty lines, although this is just a rare/contrived corner case. - LibSVM: when {{numFeature}} is not set, we need to scan the whole dataset to infer the total number of features to construct result {{LabeledPoint}}s. Unfortunately, with our current API, this kind of global information can't be gathered. The solution proposed here is to add a {{prepareRead}} method, which accepts the same arguments as {{inferSchema}} but returns a {{ReadContext}}, which contains an {{Option\[StructType\]}} for the inferred schema and a {{Map\[String, Any\]}} for any gathered global information. This {{ReadContext}} is then passed to {{buildReader()}}. By default, {{prepareRead}} simply calls {{inferSchema}} (actually the inferred schema itself can be considered as a sort of global information). -- This message was sent by Atlassian JIRA (v6.3.4#6332) --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@spark.apache.org For additional commands, e-mail: issues-h...@spark.apache.org