Remove the pre-update lock on a user's attribute rows - #4624
Remove the pre-update lock on a user's attribute rows#4624sadilchamishka wants to merge 4 commits into
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WalkthroughChangesClaim update optimization
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to The PR removes a serialization lock and makes claim updates seekable, but the new SQL Server index must be created before this build is deployed; reversing that order can cause concurrent claim updates to fail with deadlocks or HTTP 500 responses. The change is mergeable with explicit deployment-owner follow-up. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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In `@distribution/kernel/carbon-home/dbscripts/mssql.sql`:
- Around line 422-423: Update the SQL Server schema logic for
UM_ATTR_USER_ID_TENANT_ID_NAME_PROFILE_INDEX to create the index only when it
does not already exist, using an idempotent conditional guard consistent with
the surrounding table-creation logic. Preserve the existing index definition and
ensure upgrades on databases where the index is already present complete without
error.
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core/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/jdbc/JDBCRealmConstants.javacore/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/jdbc/UniqueIDJDBCUserStoreManager.javacore/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/util/JDBCRealmUtil.javacore/org.wso2.carbon.user.core/src/test/java/org/wso2/carbon/user/core/jdbc/ClaimUpdatePredicateSQLTest.javadistribution/kernel/carbon-home/dbscripts/mssql.sql
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Pull request overview
This PR addresses SQL Server deadlocks and long waits during concurrent updates of different user claims by making the update predicate seekable (SQL Server–specific casting), enforcing deterministic batch ordering, and adding a supporting composite index so updates lock only the row they modify instead of a whole user’s attribute range.
Changes:
- Added a composite index on
UM_USER_ATTRIBUTEto support the seekable predicate used by claim reads/writes on SQL Server. - Introduced a SQL Server–specific optimized update statement that casts parameters to
VARCHAR, and registered it as a DB-specific default without overriding user-provided SQL. - Ensured deterministic claim batch ordering (by claim URI) and added tests to pin the SQL Server statement shape and ordering behavior.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| distribution/kernel/carbon-home/dbscripts/mssql.sql | Adds a new composite index intended to support seekable claim updates/reads on SQL Server. |
| core/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/jdbc/JDBCRealmConstants.java | Adds SQL Server–specific optimized update SQL and property key; documents rationale. |
| core/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/util/JDBCRealmUtil.java | Registers the SQL Server optimized update as a default without overriding configured SQL. |
| core/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/jdbc/UniqueIDJDBCUserStoreManager.java | Orders claim batches deterministically and removes the pre-update UPDLOCK approach. |
| core/org.wso2.carbon.user.core/src/test/java/org/wso2/carbon/user/core/jdbc/ClaimUpdatePredicateSQLTest.java | Adds tests to guard the SQL Server statement casts, parameter ordering, and batch ordering. |
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…ttribute update for mssql
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Pull request overview
Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.
Suppressed comments (1)
core/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/jdbc/UniqueIDJDBCUserStoreManager.java:3287
- The PR description states that removing the pre-update lock is only safe when the new index is present; however, updateProperties no longer performs any pre-locking and there is no runtime guard that prevents this path from running against an unindexed SQL Server database. To avoid reintroducing ~100+ deadlocks in that scenario, consider keeping the old UPDLOCK pre-lock (or another safety fallback) unless the required index is detected / the MSSQL-optimized statement is guaranteed to be used.
String sqlStmt =
realmConfig.getUserStoreProperty(JDBCRealmConstants.UPDATE_USER_PROPERTY_WITH_ID + "-" + type);
if (sqlStmt == null) {
sqlStmt = realmConfig
.getUserStoreProperty(JDBCRealmConstants.UPDATE_USER_PROPERTY_WITH_ID_OPTIMIZED + "-" + type);
Review feedback: the CREATE INDEX was unguarded, so re-running the script against a database that already has the index failed. Guarded with a SYS.INDEXES check rather than the drop-and-recreate pattern used above it, so provisioning a database that already has the index is a no-op instead of rebuilding it.
Verified against a running server rather than against statements: with
the new index in place, the plain statement already seeks on all four
predicate columns, so casting the parameters adds nothing.
The execution plan the server actually used for the uncast statement,
read back from the plan cache after real SCIM PATCH traffic:
Index Seek UM_USER_ATTRIBUTE UM_ATTR_USER_ID_TENANT_ID_NAME_PROFILE_INDEX
estimatedRowsRead = 1.88
SeekPredicates: UM_USER.UM_ID, @p5, @p1, @p2
no residual predicate, no CONVERT_IMPLICIT
Four seek keys, no conversion on the column. The UM_USER lookup seeks
its unique index as well.
That holds because the deployment sets sendStringParametersAsUnicode=false
on the user store datasource, so the driver already sends varchar and
there is no conversion left to move off the column. 128 concurrent SCIM
claim updates of one user at 8, 16 and 32 threads: all succeeded, and
SQL Server recorded no new deadlocks.
What remains is the index and the deterministic batch order. Both are
required: with the index dropped, the same build fails 45 of 128 requests
at 32 threads with HTTP 500 and records 66 deadlocks.
Note for deployments that do not set that property - stock installations
have no default for it - the predicate is still not seekable and this
build should not be run without setting it.
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Pull request overview
Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.
Suppressed comments (1)
core/org.wso2.carbon.user.core/src/main/java/org/wso2/carbon/user/core/jdbc/UniqueIDJDBCUserStoreManager.java:3306
- The SQL Server deadlock mitigation now relies on the UPDATE predicate being seekable on (UM_USER_ID, UM_TENANT_ID, UM_ATTR_NAME, UM_PROFILE_ID). In this batch loop, UM_ATTR_NAME and UM_PROFILE_ID are always bound via setString (only UM_ATTR_VALUE uses setNString when unicode storage is enabled). On SQL Server, if the JDBC driver sends these as NVARCHAR (e.g., when sendStringParametersAsUnicode is not set to false), the comparison to VARCHAR columns can become unseekable even with the new index, reintroducing the deadlock/outage scenario described in the PR.
Consider making the predicate seekable regardless of that datasource setting (e.g., MSSQL-specific SQL that CASTs the UM_ATTR_NAME / UM_PROFILE_ID parameters to VARCHAR, or an MSSQL-only binding that forces VARCHAR types for those parameters), or at minimum emitting a one-time WARN when running against SQL Server without a configuration that guarantees VARCHAR parameters.
}
boolean useNString = shouldUseNString(dbConnection);
prepStmt = dbConnection.prepareStatement(sqlStmt);
for (Map.Entry<String, String> entry : orderClaimsForBatch(properties)) {
String propertyName = entry.getKey();
String propertyValue = entry.getValue();
if (sqlStmt.contains(UserCoreConstants.UM_TENANT_COLUMN)) {
Removing it made this change depend on sendStringParametersAsUnicode being false on the user store datasource. That holds where it is set, but the Helm chart still defaults it to true and stock installations have no default for it at all - and where the driver sends nvarchar the conversion lands on the VARCHAR column, the predicate cannot seek, and the index alone does not prevent the deadlock. Casting the parameter keeps the locking behaviour correct either way, and costs nothing where the property is already set: same plan, same four-column seek, same throughput. Unrelated to Unicode support, which is handled separately by StoreUserAttributeValueAsUnicode binding UM_ATTR_VALUE with setNString. The cast never applied to that column.
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PR builder started |
| public static final String UPDATE_USER_PROPERTY_WITH_ID_OPTIMIZED_SQL = "UPDATE UM_USER_ATTRIBUTE SET UM_ATTR_VALUE=? " + | ||
| "WHERE UM_ATTR_NAME=? AND UM_PROFILE_ID=? AND UM_USER_ID=(SELECT UM_ID FROM UM_USER WHERE UM_USER_ID=? AND " + | ||
| "UM_TENANT_ID=?) AND UM_TENANT_ID=?"; | ||
| public static final String UPDATE_USER_PROPERTY_WITH_ID_OPTIMIZED_MSSQL_SQL = "UPDATE UM_USER_ATTRIBUTE SET " + |
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There can be cases sql connection is configured with parameters SendStringParametersAsUnicode=true when unicode support is provided.
Though unicodes are supported for values, the keys will be still not unicode characters. Hence this change avoid the jdbc driver to convert them to nvarchar which then cause to miss the indexes which have been configured according to their data type of varchar.
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Approving the pull request based on the successful pr build https://github.com/wso2/product-is/actions/runs/32805886000
Issue
Concurrent updates to different claims of the same user serialise on SQL Server. Before batch updating a user's claims the SQL Server path takes a
SELECT ... WITH (UPDLOCK)over every attribute row of that user and holds it until commit, so updates to one user run strictly one at a time.The lock is there because the batch would otherwise deadlock with itself. No index carries
UM_ATTR_NAMEorUM_PROFILE_IDin its key — the covering index has them only asINCLUDEcolumns, which take no part in the B-tree ordering — so an update of one claim cannot seek to its own row. It reads the user's whole attribute range and locks every row of it. See wso2/product-is#21302.sequenceDiagram autonumber participant A as Tx A — mobile, then email participant DB as the user's attribute rows,<br/>scanned in index order: … email … mobile … participant B as Tx B — email, then country A->>DB: statement 1 — UPDATE 'mobile' Note over A,DB: scan passes 'email' — U taken, no match, released.<br/>Reaches 'mobile': U converts to X, held until commit. B->>DB: statement 1 — UPDATE 'email' Note over DB,B: reaches 'email': X, held until commit.<br/>The predicate is residual, so the scan cannot stop here —<br/>it must continue and test every remaining row. DB--xB: scan continues to 'mobile' → needs U, Tx A holds X Note over DB,B: Tx B is blocked inside statement 1,<br/>while already holding X on 'email' A->>DB: statement 2 — UPDATE 'email' DB--xA: scan reaches 'email' → needs U, Tx B holds X Note over A,B: A waits on 'email', B waits on 'mobile' — the wait graph closes DB->>B: error 1205, Tx B chosen as victimUis the update lock SQL Server takes while searching for the row to modify, and it is incompatible with another transaction'sX. Locking happens at the access-path level, not the predicate level: the residual predicate filters rows only after they have been locked. So each transaction blocks on rows it never writes.The residual predicate is also why a statement cannot stop at its target: it has no way to know that
row was the only match, so it keeps scanning — and requests locks on later rows while already holding
Xon its own. That is the edge that closes the cycle, and it needs two statements to do it. With oneclaim per transaction the same workload records 0 deadlocks in 200; with two, 149.
How the current
WITH (UPDLOCK)pre-select prevents this, and what it costssequenceDiagram autonumber participant A as Tx A — mobile, email participant DB as the user's attribute rows participant B as Tx B — email, country A->>DB: SELECT UM_ID … WITH (UPDLOCK) … ORDER BY UM_ID Note over A,DB: one statement takes U on every row of the user,<br/>held until commit — and it runs before any of A's writes B->>DB: SELECT UM_ID … WITH (UPDLOCK) — the same rows DB--xB: blocked on the very first row: U conflicts with U Note over B,DB: B waits holding nothing at all.<br/>No edge points back from B, so the wait graph cannot close. A->>DB: UPDATE 'mobile' → U converts to X, A already owns the row A->>DB: UPDATE 'email' → U converts to X A->>DB: COMMIT — releases all rows DB->>B: acquires the whole set, then runs its own updatesThe deadlock needs partial, interleaved lock sets — each transaction holding one row while requesting
another. The pre-select makes acquisition atomic: one statement, all rows, before any write. A
transaction therefore holds the whole set or none of it, and the loser blocks holding nothing, so it
cannot be one end of a cycle. It also removes the enabler above: once a transaction owns
Uon everyrow, its updates only convert
U → Xon rows it already holds, and continuing the scan past its targettouches nothing it does not own.
Two details are load-bearing.
ORDER BY UM_IDmatters because two pre-selects scanning in oppositeorders could still deadlock with each other — one holding the first row and wanting the last, the other
the reverse. And
Uconflicting withUis what makes the second pre-select block; shared locks wouldlet both through.
The cost is that every concurrent update of one user runs strictly one at a time, for the whole batch
plus commit. The deadlock becomes a queue — which is the ~47 tps plateau measured through SCIM
regardless of concurrency, and the tens-of-seconds waits in the original report. The lock is not wrong;
it is the correct remedy for a statement whose footprint is the whole user. This PR removes the need for
it rather than removing the protection.
Fix
Two changes, then the lock goes:
(UM_USER_ID, UM_TENANT_ID, UM_ATTR_NAME, UM_PROFILE_ID) INCLUDE (UM_ATTR_VALUE)— theclaim name and profile move from
INCLUDEinto the key, so the statement seeks to the one row itwrites.
could take the same row locks in opposite orders.
WITH (UPDLOCK)pre-select. The statements stay registered as user storeproperties for configuration compatibility; nothing executes them.
sequenceDiagram autonumber participant A as Tx A — email, mobile participant DB as the user's attribute rows,<br/>4-column key: the seek range IS one row participant B as Tx B — country, email Note over A,B: both batches ordered by claim URI, so locks are taken in one global sequence A->>DB: UPDATE 'email' → seek, 1 row, X on 'email' B->>DB: UPDATE 'country' → seek, 1 row, X on 'country' Note over A,DB: no scan continuation — nothing is locked beyond the row being written B->>DB: UPDATE 'email' → needs 'email', which Tx A actually writes Note over A,B: a plain wait, not a cycle: A holds one row and needs nothing B holds A->>DB: UPDATE 'mobile' → X on 'mobile', then COMMIT — releases both DB->>B: proceeds, then commitsTwo independent things remove the cycle, which is why the result is robust rather than lucky. The seek
range is the row, so a transaction never holds one row while requesting another mid-statement. And the
sorted batch gives a global acquisition order, so a waiting transaction always waits on one that is not
waiting on it. Genuine contention on the same claim still serialises on that row, which is correct.
Verification
Measured through real
PATCH /scim2/Users/{id}calls against a running server. 128 concurrent SCIMclaim updates of a single user:
The plan explains the difference. Both are reported as
Index Seek; only the range differs:UM_ATTR_NAME/UM_PROFILE_IDImportant
The index must be created before this build is deployed. On a database without it, removing the
lock fails 21–35 % of concurrent claim updates. The reverse order is safe — the current build
against an already-indexed database is unaffected.
Why the cast is in this PR
The two changes above are enough only where the datasource sets
sendStringParametersAsUnicode=false. Where it does not — the driver sendsnvarchar, the conversionlands on the
VARCHARcolumn, and the two extra key columns become unusable again.Measured through real SCIM calls on an
nvarchardatasource, with the new index present in bothrows:
The plans say why. Without it the predicate is residual:
With it the conversion moves onto the parameter and stays seekable:
Where the property is set the cast is a no-op — same four-column seek, same throughput — so it costs
nothing and makes the fix correct under either datasource configuration.
A related configuration requirement, not caused by this change
sendStringParametersAsUnicode=falsealso makes the driver send claim values asvarchar, soStoreUserAttributeValueAsUnicode=truemust be set on the user store or non-ASCII claim values aredestroyed at write time. Verified on a running server:
松本 明子stored as?? ??without it, intactwith it, at no cost to the seek. That property gates
setNStringonUM_ATTR_VALUEonly; the castnever applied to that column, so the two are independent.