From 4958e1d60f2528be6ef1109bc562139b2c1f4120 Mon Sep 17 00:00:00 2001
From: Timm Fitschen <t.fitschen@indiscale.com>
Date: Fri, 26 Feb 2021 10:13:35 +0100
Subject: [PATCH] EHN: ETag property for the Query
---
CHANGELOG.md | 4 ++++
.../java/org/caosdb/server/query/Query.java | 21 +++++++++++++++----
2 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 76e20e39..dceac0e2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
### Added
+* `ETag` property for the query. The `ETag` tags a server state and is being
+ updated each time the server state is being updated (i.e. the stored entities
+ change). This can be used to debug the query cache and also allows a client
+ to determine whether the server's state has changed between queries.
* Basic caching for queries. The caching is enabled by default and can be
controlled by the usual "cache" flag.
diff --git a/src/main/java/org/caosdb/server/query/Query.java b/src/main/java/org/caosdb/server/query/Query.java
index 0a877fc8..60c361be 100644
--- a/src/main/java/org/caosdb/server/query/Query.java
+++ b/src/main/java/org/caosdb/server/query/Query.java
@@ -39,6 +39,7 @@ import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
+import java.util.UUID;
import org.antlr.v4.runtime.CharStreams;
import org.antlr.v4.runtime.CommonTokenStream;
import org.apache.commons.jcs.access.behavior.ICacheAccess;
@@ -238,6 +239,14 @@ public class Query implements QueryInterface, ToElementable, TransactionInterfac
*/
private boolean cachable = true;
+ /**
+ * Tags the query cache and is renewed each time the cache is being cleared, i.e. each time the
+ * database is being updated.
+ *
+ * <p>As the name suggests, the idea is similar to the ETag header of the HTTP protocol.
+ */
+ private static String cacheETag = UUID.randomUUID().toString();
+
public Type getType() {
return this.type;
}
@@ -668,6 +677,7 @@ public class Query implements QueryInterface, ToElementable, TransactionInterfac
/** Remove all cached queries from the cache. */
public static void clearCache() {
+ cacheETag = UUID.randomUUID().toString();
cache.clear();
}
@@ -678,10 +688,12 @@ public class Query implements QueryInterface, ToElementable, TransactionInterfac
* @param resultSet
*/
private void setCache(String key, List<IdVersionPair> resultSet) {
- if (resultSet instanceof Serializable) {
- cache.put(key, (Serializable) resultSet);
- } else {
- cache.put(key, new ArrayList<>(resultSet));
+ synchronized (cache) {
+ if (resultSet instanceof Serializable) {
+ cache.put(key, (Serializable) resultSet);
+ } else {
+ cache.put(key, new ArrayList<>(resultSet));
+ }
}
}
@@ -859,6 +871,7 @@ public class Query implements QueryInterface, ToElementable, TransactionInterfac
ret.setAttribute("results", "0");
}
ret.setAttribute("cached", Boolean.toString(this.cached));
+ ret.setAttribute("etag", cacheETag);
final Element parseTreeElem = new Element("ParseTree");
if (this.el.hasErrors()) {
--
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