[Issue #163]: fix bounded varchar/char type support. (#165)

Modify PixelsTypeManager in pixels-presto to fix this issue.

README.md

@@ -75,10 +75,12 @@ To use the columnar cache in Pixels (i.e., pixels-cache), create and mount an in
 sudo mkdir -p /mnt/ramfs
 sudo mount -t tmpfs -o size=1g tmpfs /mnt/ramfs
 ```
+The path `/mnt/ramfs` is determined by `cache.location` and `index.location` in `PIXELS_HOME/pixels.properties`.
 The `size` parameter of the mount command should be larger than or equal to the sum of `cache.size` and `index.size` in 
 `PIXELS_HOME/pixels.properties`. And it must be smaller than the physical memory size.
 Also ensure that `cache.enabled` and `cache.read.direct` are set to `true` in `PIXELS_HOME/pixels.properties`.
-Set `cache.enabled` to `false` if you don't want to use pixels-cache.
+Set `cache.enabled` to `false` if you don't want to use pixels-cache. 
+But **NOTE** that the path `/mnt/ramfs` must exist even if pixels-cache is disabled, as Pixels checks this path when starts.
 
 ### Install MySQL
 MySQL and etcd are used to store the metadata and states of Pixels. To install MySQL:

pixels-common/src/main/java/io/pixelsdb/pixels/common/metadata/domain/Column.java

@@ -54,6 +54,10 @@ public void setName(String name)
         this.name = name;
     }
 
+    /**
+     * Get the full type's display name, e.g., integer, varchar(10).
+     * @return
+     */
     public String getType()
     {
         return type;

pixels-presto/src/main/java/io/pixelsdb/pixels/presto/PixelsTypeManager.java

@@ -81,21 +81,41 @@ public static <A, B extends A> B checkObjectType(A value, Class<B> target, Strin
         signatureToType = new HashMap<>();
         for (Type type : supportedTypes)
         {
-            signatureToType.put(type.getDisplayName(), type);
+            /**
+             * Issue #163:
+             * Register the lowercase of the type's display name.
+             */
+            signatureToType.put(type.getDisplayName().toLowerCase(), type);
         }
+        /**
+         * Issue #163:
+         * Support char(n) using varchar.
+         */
+        signatureToType.put("char", VARCHAR);
     }
 
     private PixelsTypeManager () {}
 
     public Type getType(String signature)
     {
-        return signatureToType.get(signature);
+        /**
+         * Issue #163:
+         * The signature in signatureToType is the prefix in lowercase of the type's display name.
+         * Fore example, varchar or char instead of varchar(10) or char(10). Therefore we use the
+         * lowercase of the prefix of the parameter to do the matching.
+         */
+        int index = signature.indexOf("(");
+        if (index > 0)
+        {
+            signature = signature.substring(0, index);
+        }
+        return signatureToType.get(signature.toLowerCase());
     }
 
     @Override
     public Type getType(TypeSignature signature)
     {
-        return signatureToType.get(signature.toString());
+        return getType(signature.toString());
     }
 
     @Override

pixels-presto/src/main/java/io/pixelsdb/pixels/presto/impl/PixelsMetadataProxy.java

@@ -19,6 +19,7 @@
  */
 package io.pixelsdb.pixels.presto.impl;
 
+import com.facebook.presto.spi.PrestoException;
 import com.facebook.presto.spi.type.Type;
 import com.google.inject.Inject;
 import io.airlift.log.Logger;
@@ -31,6 +32,7 @@
 import io.pixelsdb.pixels.common.utils.ConfigFactory;
 import io.pixelsdb.pixels.presto.PixelsColumnHandle;
 import io.pixelsdb.pixels.presto.PixelsTypeManager;
+import io.pixelsdb.pixels.presto.exception.PixelsErrorCode;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -86,7 +88,8 @@ public List<PixelsColumnHandle> getTableColumn(String connectorId, String schema
             Type columnType = PixelsTypeManager.getColumnType(c);
             if (columnType == null)
             {
-                log.error("columnType is not defined.");
+                throw new PrestoException(PixelsErrorCode.PIXELS_METASTORE_ERROR,
+                        "columnType '" + c.getType() + "' is not defined.");
             }
             String name = c.getName();
             PixelsColumnHandle pixelsColumnHandle = new PixelsColumnHandle(connectorId, name, columnType, "", i);