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Better javadoc UnfilteredSerializer 

patch by weideng; reviewed by slebresne for CASSANDRA-11640
This commit is contained in:
Wei Deng 2016-04-25 03:12:59 +00:00 committed by Sylvain Lebresne
parent fe7eee0066
commit aefa580d09
1 changed files with 57 additions and 39 deletions
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96
src/java/org/apache/cassandra/db/rows/UnfilteredSerializer.java
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@ -28,46 +28,62 @@ import org.apache.cassandra.io.util.DataOutputPlus;
/**
* Serialize/deserialize a single Unfiltered (both on-wire and on-disk).
* <p>
*
* {@code
* The encoded format for an unfiltered is <flags>(<row>|<marker>) where:
*
* <flags> is a byte (or two) whose bits are flags used by the rest of the serialization. Each
* flag is defined/explained below as the "Unfiltered flags" constants. One of those flags
* is an extension flag, and if present, trigger the rid of another byte that contains more
* flags. If the extension is not set, defaults are assumed for the flags of that 2nd byte.
* <row> is <clustering><size>[<timestamp>][<ttl>][<deletion>]<sc1>...<sci><cc1>...<ccj> where
* <clustering> is the row clustering as serialized by {@code Clustering.serializer} (note
* that static row are an exception and don't have this).
* <size> is the size of the whole unfiltered on disk (it's only used for sstables and is
* used to efficiently skip rows).
* <timestamp>, <ttl> and <deletion> are the row timestamp, ttl and deletion
* whose presence is determined by the flags. <sci> is the simple columns of the row and <ccj> the
* complex ones.
* The columns for the row are then serialized if they differ from those in the header,
* and each cell then follows:
* * Each simple column <sci> will simply be a <cell>
* (which might have no value, see below),
* * Each <ccj> will be [<delTime>]<n><cell1>...<celln> where <delTime>
* is the deletion for this complex column (if flags indicates it present), <n>
* is the vint encoded value of n, i.e. <celln>'s 1-based index, <celli>
* are the <cell> for this complex column
* <marker> is <bound><deletion> where <bound> is the marker bound as serialized
* by {@code ClusteringBoundOrBoundary.serializer} and <deletion> is the marker deletion
* time.
*
* <cell> A cell start with a 1 byte <flag>. The 2nd and third flag bits indicate if
* it's a deleted or expiring cell. The 4th flag indicates if the value
* is empty or not. The 5th and 6th indicates if the timestamp and ttl/
* localDeletionTime for the cell are the same than the row one (if that
* is the case, those are not repeated for the cell).Follows the <value>
* (unless it's marked empty in the flag) and a delta-encoded long <timestamp>
* (unless the flag tells to use the row level one).
* Then if it's a deleted or expiring cell a delta-encoded int <localDelTime>
* and if it's expiring a delta-encoded int <ttl> (unless it's an expiring cell
* and the ttl and localDeletionTime are indicated by the flags to be the same
* than the row ones, in which case none of those appears).
* }
* The encoded format for an unfiltered is {@code <flags>(<row>|<marker>)} where:
* <ul>
* <li>
* {@code <flags>} is a byte (or two) whose bits are flags used by the rest
* of the serialization. Each flag is defined/explained below as the
* "Unfiltered flags" constants. One of those flags is an extension flag,
* and if present, indicates the presence of a 2ndbyte that contains more
* flags. If the extension is not set, defaults are assumed for the flags
* of that 2nd byte.
* </li>
* <li>
* {@code <row>} is
* {@code <clustering><sizes>[<pkliveness>][<deletion>][<columns>]<columns_data>}
* where:
* <ul>
* <li>{@code <clustering>} is the row clustering as serialized by
* {@link Clustering.serializer} (note that static row are an
* exception and don't have this). </li>
* <li>{@code <sizes>} are the sizes of the whole unfiltered on disk and
* of the previous unfiltered. This is only present for sstables and
* is used to efficiently skip rows (both forward and backward).</li>
* <li>{@code <pkliveness>} is the row primary key liveness infos, and it
* contains the timestamp, ttl and local deletion time of that info,
* though some/all of those can be absent based on the flags. </li>
* <li>{@code deletion} is the row deletion. It's presence is determined
* by the flags and if present, it conists of both the deletion
* timestamp and local deletion time.</li>
* <li>{@code <columns>} are the columns present in the row encoded by
* {@link Columns.serializer#serializeSubset}. It is absent if the row
* contains all the columns of the {@code SerializationHeader} (which
* is then indicated by a flag). </li>
* <li>{@code <columns_data>} is the data for each of the column present
* in the row. The encoding of each data depends on whether the data
* is for a simple or complex column:
* <ul>
* <li>Simple columns are simply encoded as one {@code <cell>}</li>
* <li>Complex columns are encoded as {@code [<delTime>]<n><cell1>...<celln>}
* where {@code <delTime>} is the deletion for this complex
* column (if flags indicates its presence), {@code <n>} is the
* vint encoded value of n, i.e. {@code <celln>}'s 1-based
* inde and {@code <celli>} are the {@code <cell>} for this
* complex column</li>
* </ul>
* </li>
* </ul>
* </li>
* <li>
* {@code <marker>} is {@code <bound><deletion>} where {@code <bound>} is
* the marker bound as serialized by {@link ClusteringBoundOrBoundary.serializer}
* and {@code <deletion>} is the marker deletion time.
* </li>
* </ul>
* <p>
* The serialization of a {@code <cell>} is defined by {@link Cell.Serializer}.
*/
public class UnfilteredSerializer
{
@ -163,6 +179,8 @@ public class UnfilteredSerializer
if (header.isForSSTable())
{
out.writeUnsignedVInt(serializedRowBodySize(row, header, previousUnfilteredSize, version));
// We write the size of the previous unfiltered to make reverse queries more efficient (and simpler).
// This is currently not used however and using it is tbd.
out.writeUnsignedVInt(previousUnfilteredSize);
}