Why is the write ops count so high for my object?

Question

I need help understanding why one of my model objects that I persist with the datastore costs so much write ops. Looking at the datastore viewer in the dev console, it says that I need 31 write ops to create this object; clicking on the Show Indexes link, I can see that there are two indexes defined for this object (as intended), and reading the documentation:

New Entity Put (per entity, regardless of entity size): 2 Writes + 2 Writes per indexed property value + 1 Write per composite index value

So, if I understand correctly, to create or delete this objects costs 2 writes + 2 Writes * 2 Indexed property value + 0 (I have no composite index value) = 6 write ops?

To modify:

Existing Entity Put (per entity) 1 Write + 4 Writes per modified indexed property value + 2 Writes per modified composite index value

should cost 1 write if non-indexed property are modified, and 5 (or 9) if one or two indexed properties are modified? I am confused as to why the dev console reports 31 write ops needed...

The object is as follows:

public class Media implements IMedia {

private static final long serialVersionUID = 1657456300412658003L;
// Get a file service
private static FileService fileService = FileServiceFactory.getFileService();

@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
@Persistent
private String title;

@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
@Persistent
private String author;

@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private Text description;

@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private MediaType mediaType;

@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private String fullPath;

@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private String fileName;
@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private long size;
@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private String contentType;
@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private boolean isDeactive;
@Persistent
private String chartId;
@Transient
private IChart chart;
@Persistent
private boolean approved;

@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key key;

@Persistent
private Date imageDate;
@Transient
private BlobKey blobKey;
@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private float imageLatitute = 190;
@Persistent
@Extension(vendorName="datanucleus", key="gae.unindexed", value="true")
private float imageLongitute = 190;

...

Answer 1

Try turning on Appstats. It gives you great insight in where your I/O cost comes from.

The other thing to think about is index writes. The more indexed properties or composite index entries you have, the most it costs to write an entity.