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new 452df84d1e JAMES-4227 Allow controlling JMAP message preview length
452df84d1e is described below
commit 452df84d1e0850f3d8f7d48b04540d9f24719f42
Author: Benoit TELLIER <[email protected]>
AuthorDate: Sat Sep 5 21:10:12 2026 +0200
JAMES-4227 Allow controlling JMAP message preview length
---
docs/modules/servers/partials/configure/jvm.adoc | 21 +++++++++++++++++++++
.../sample-configuration/jvm.properties | 5 +++++
.../org/apache/james/jmap/api/model/Preview.java | 20 +++++++++++++++++++-
3 files changed, 45 insertions(+), 1 deletion(-)
diff --git a/docs/modules/servers/partials/configure/jvm.adoc
b/docs/modules/servers/partials/configure/jvm.adoc
index 76cfa72e55..e2418d40af 100644
--- a/docs/modules/servers/partials/configure/jvm.adoc
+++ b/docs/modules/servers/partials/configure/jvm.adoc
@@ -78,6 +78,27 @@ james.blob.id.hash.encoding=base16
Optional. String. Defaults to base64Url.
+== Change the length of JMAP previews
+
+A JMAP preview keeps the first 256 characters of the text body of a message,
so that clients can render a
+message list without fetching bodies. The property `james.jmap.preview.length`
changes that, in
+characters.
+
+Ex in `jvm.properties`
+----
+james.jmap.preview.length=128
+----
+
+Optional. Strictly positive integer. Defaults to 256.
+
+Previews are the heaviest per message projection James stores in Cassandra,
ahead of any single mailbox
+metadata column, so halving them is the shortest path to a smaller
`messageFastViewProjection` table.
+Weigh it against how many characters your JMAP clients actually display: most
message lists show two
+lines at most.
+
+Lowering it only affects previews computed afterwards. Those already stored
keep their length until the
+message is reindexed, so the space comes back progressively rather than at
once.
+
== Improve listing support for MinIO
Due to blobs being stored in folder, adding `/` in blobs name emulates folder
and avoids blobs to be all stored in a
diff --git a/server/apps/distributed-app/sample-configuration/jvm.properties
b/server/apps/distributed-app/sample-configuration/jvm.properties
index 4c1ce91297..ce4087873b 100644
--- a/server/apps/distributed-app/sample-configuration/jvm.properties
+++ b/server/apps/distributed-app/sample-configuration/jvm.properties
@@ -96,6 +96,11 @@ jmx.remote.x.mlet.allow.getMBeansFromURL=false
# Be careful turning on this as `%` and `*` are ambiguous for the LIST / LSUB
commands that interpret those as wildcard thus returning all mailboxes matching
the pattern.
#james.relaxed.mailbox.name.validation=true
+# Characters of the text body kept in a JMAP preview. Strictly positive,
defaults to 256.
+# Previews are the heaviest per message projection stored in Cassandra:
halving this halves the
+# messageFastViewProjection table. Only applies to previews computed
afterwards.
+# james.jmap.preview.length=128
+
# Count of octet from which hashing shall be done out of the IO threads in
deduplicating blob store
# james.deduplicating.blobstore.thread.switch.threshold=32768
# Count of octet from which streams are buffered to files and not to memory
diff --git
a/server/data/data-jmap/src/main/java/org/apache/james/jmap/api/model/Preview.java
b/server/data/data-jmap/src/main/java/org/apache/james/jmap/api/model/Preview.java
index 53c923498f..6faaad5645 100644
---
a/server/data/data-jmap/src/main/java/org/apache/james/jmap/api/model/Preview.java
+++
b/server/data/data-jmap/src/main/java/org/apache/james/jmap/api/model/Preview.java
@@ -89,7 +89,25 @@ public class Preview {
public static final Preview EMPTY = Preview.from("");
- private static final int MAX_LENGTH = 256;
+ public static final String MAX_LENGTH_PROPERTY =
"james.jmap.preview.length";
+ public static final int DEFAULT_MAX_LENGTH = 256;
+
+ /**
+ * How many characters of the text body a preview keeps.
+ *
+ * <p>Previews are the heaviest per message projection James stores, so
shortening them is a
+ * straightforward way to trade list rendering for storage. Lowering it
only affects previews computed
+ * afterwards: the ones already stored keep their length until they are
recomputed.</p>
+ */
+ private static final int MAX_LENGTH = maxLength();
+
+ @VisibleForTesting
+ static int maxLength() {
+ int maxLength = Integer.getInteger(MAX_LENGTH_PROPERTY,
DEFAULT_MAX_LENGTH);
+ Preconditions.checkArgument(maxLength > 0,
+ "'%s' must be strictly positive, got %s", MAX_LENGTH_PROPERTY,
maxLength);
+ return maxLength;
+ }
public static Preview from(String value) {
return new Preview(value);
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