After a 2½-year pause, SAP chief executive Bill McDermott is buying again. Last week,  he landed the latest in an almost-yearly string of $1 billion-plus acquisitions, seeking to keep the Germany-based business-software giant relevant amid fast-morphing technologies and flush rivals.

SAP, with $24 billion in yearly sales, employs 90,000 worldwide, including 3,000 management, sales, marketing and tech people at its U.S. headquarters in Newtown Square.

SAP said it will buy Callidus Software Inc., a California company that sells systems for planning and tracking business sales and incentives, for $2.3 billion — more than 10 times publicly traded Callidus' yearly revenues.

Callidus competes in what McDermott and software marketers call "sales performance management" — SPM — whose sector sales should top $1 billion next year, according to Gartner Group of Stamford, Conn.

SAP, founded by four German ex-IBM engineers in 1972, used to make all its own software — big, expensive systems that European firms especially used to manage corporate income and spending, forcing clients' employees to learn its arcane language.

As the spread of smartphones and remote (cloud) servers enabled a host of new, cheap, specialized rival business applications,  McDermott, a former star Xerox salesman hired to run SAP's U.S. division in 2002, pushed SAP directors to buy rising data-systems and cloud-based companies, instead of building from scratch.

He championed SAP's $5.2 billion acquisition of artificial-intelligence developer Business Objects in 2007 and Sybase in 2010 ($5.3 billion) along with SAP's ensuing development of the Hana in-memory database-management systems and the S/4 Hana business suite that SAP says customers are rapidly adopting.

Investors have bought in. Since McDermott was named co-CEO in 2010 (he's been sole CEO since 2014), the company's share price is up an average 14 percent a year, beating Oracle (12 percent) and IBM (6 percent). SAP also trades at a higher multiple to its profits than those big rivals, a sign investors expect it will keep boosting sales.

But SAP has also trailed smaller, cloud-era specialist rivals such as Salesforce, whose returns on McDermott's watch have doubled SAP's. Since early 2015, SAP has accelerated and Salesforce has slowed: both have averaged 18 percent.

Wall Street pros love mergers because they mean fat paydays for investment bankers, lawyers, and executives who reap deal bonuses. They also allow CEOs  and CFOs an easy explanation for higher expenses and temporarily weak profits.

But deals are risky for shareholders; veteran software-company analysts are used to exaggeration and evaporating deal profits. It wasn't surprising that McDermott promised to lay off M&A for awhile in 2014 after SAP's biggest-ever deal, its $7.2 billion acquisition of Concur Technology, purveyor of travel-and-entertainment-spending accounting.

And now, following the Callidus deal, software investors should also "take a pause" before buying more SAP shares, analyst Brian Schwartz of Oppenheimer & Co. advised clients last week. Schwartz likes Callidus. But with the steep price SAP is paying, he expects the deal will "overhang" SAP shares like a dark cloud until SAP can show sales and profits actually rise to justify the higher costs.

Analysts on the company's quarterly conference call last week also pressed McDermott about profits and prices paid. SAP will need to accelerate sales growth to hit McDermott's optimistic targets, said UBS managing director Michael J. Briest.

McDermott parried concerns by citing unidentified CEOs he talked to at last month's annual  Davos, Switzerland, conclave of billionaires, bosses and politicians: These days, corporate leaders are "ready to run simple," buying linked software products from big vendors such as SAP, instead of cherry-picking from specialty firms, he told the analysts.

Buying a software company whose users are salespeople is great exposure, he added: "We are now in the sales professional's pipeline," adding "a piece of DNA we hadn't covered before." It would have taken "too long to build it" without making the acquisition, McDermott added.

But "it took some time" for SAP to build profits from SuccessFactors and Ariba, McDermott's first acquisitions as CEO, Goldman Sachs analyst Mohammed E. Moawalla reminded the CEO.

"The show's on the road," McDermott insisted, bragging about new customers for SAP Concur (such as Vodaphone, Barclays Bank), for Ariba, the $4.3 billion procurement-software company that SAP bought in 2012 (which recently signed up Ford and Coca-Cola), and for SuccessFactors Inc., the hiring and personnel software company that SAP bought for $3.3 billion in 2011 (which recently added Apple supplier Foxconn and building-materials giant AkzoNobel).

Among the people made happiest by SAP's latest deal are the heads of upstart companies Gartner lists as competitors to SAP-Callidus, Oracle and IBM in the sales-performance business. The deal is proof their industry "is poised for explosive growth," emailed Mark Stiffler, CEO of Optymyze.

Another sales performance rival, San Francisco-based Anaplan, is "taking business away from legacy providers" such as SAP — and Callidus, too, says Anaplan chief revenue officer Paul Melchiorre, a South Philly native and Villanova grad who learned the business in what's now McDermott's shop, as a former executive at Ariba and SAP.

(This column has been updated to correct the acquisition sequence)