Github user arina-ielchiieva commented on a diff in the pull request: https://github.com/apache/drill/pull/685#discussion_r98186438 --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/impl/ContextFunctions.java --- @@ -64,17 +65,45 @@ public void eval() { @Inject DrillBuf buffer; @Workspace int currentSchemaBytesLength; + @Override public void setup() { final byte[] currentSchemaBytes = contextInfo.getCurrentDefaultSchema().getBytes(); buffer = buffer.reallocIfNeeded(currentSchemaBytes.length); currentSchemaBytesLength= currentSchemaBytes.length; buffer.setBytes(0, currentSchemaBytes); } + @Override public void eval() { out.start = 0; out.end = currentSchemaBytesLength; out.buffer = buffer; } } + + /** + * Implement "session_id" function. Returns the unique id of the current session. + */ + @FunctionTemplate(name = "session_id", scope = FunctionTemplate.FunctionScope.SIMPLE, isNiladic = true) --- End diff -- Each drill function is converted to DrillFunctionHolder and though Calcite recognizes current_time/current_date & other context functions (ex: user, current_schema) as niladic, after introduction of isNilladic flag, DrillFunctionHolder would describe such functions as non-niladic, though they are. So we are intentionally hold incorrect info. Let's say in future I would need to take list of all function holders in Drill (form local function registry) and filter out all niladic functions, since we do have such isNiladic flag I would assume that I can use this flag as filter but since current_time/current_date & other context functions (ex: user, current_schema) have isniladic=false, they would never be filtered out. Also please add `isNiladic=true` to other niladic context functions [1]. [1] https://github.com/apache/drill/blob/5a4ad2a88331dfe7561ee76fc87e882afe170681/exec/java-exec/src/main/java/org/apache/drill/exec/expr/fn/impl/ContextFunctions.java
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