DfsGarbageCollector: Add setter for reflog expiration time.

JGit reftable writer/compator knows how to prune the history, but the
DfsGarbageCollector doesn't expose the time limit.

Add a method to DfsGarbageCollector to set the reflog time limit.
This value is then passed to the reftable compactor. Callers usually
pass here the value from gc.reflogExpire.

The reflog block length is stored in 24 bits [1], limiting the size to
16MB. I have observed that in repositories with frequent commits,
reflogs hit that size in 6-12 months.

[1] https://git-scm.com/docs/reftable

Bug: jgit-96

Change-Id: I8b32d6d2b2e1d8af8fb7d9f86225d75f1877eb2f

1 files changed, 21 insertions, 0 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
index a177669788..91440a6498 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsGarbageCollector.java
@@ -29,6 +29,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Calendar;
 import java.util.Collection;
+import java.util.Date;
 import java.util.EnumSet;
 import java.util.GregorianCalendar;
 import java.util.HashSet;
@@ -100,6 +101,7 @@ public class DfsGarbageCollector {
 	private Set<ObjectId> allTags;
 	private Set<ObjectId> nonHeads;
 	private Set<ObjectId> tagTargets;
+	private Date refLogExpire;
 
 	/**
 	 * Initialize a garbage collector.
@@ -200,6 +202,22 @@ public class DfsGarbageCollector {
 		return this;
 	}
 
+
+	/**
+	 *  Set time limit to the reflog history.
+         *  <p>
+         *  Garbage Collector prunes entries from reflog history older than {@code refLogExpire}
+         *  <p>
+	 *
+	 * @param refLogExpire
+	 *            instant in time which defines refLog expiration
+	 * @return {@code this}
+	 */
+	public DfsGarbageCollector setRefLogExpire(Date refLogExpire) {
+		this.refLogExpire = refLogExpire ;
+		return this;
+	}
+
 	/**
 	 * Set maxUpdateIndex for the initial reftable created during conversion.
 	 *
@@ -741,6 +759,9 @@ public class DfsGarbageCollector {
 			compact.addAll(stack.readers());
 			compact.setIncludeDeletes(includeDeletes);
 			compact.setConfig(configureReftable(reftableConfig, out));
+			if(refLogExpire != null ){
+				compact.setReflogExpireOldestReflogTimeMillis(refLogExpire.getTime());
+			}
 			compact.compact();
 			pack.addFileExt(REFTABLE);
 			pack.setReftableStats(compact.getStats());